So I have been in a long journey looking to find the best amplifiers for my martin logan montis. As you know, the match between an amplifier and speakers has to be a good "marriage" and needs to be blend exquisitely. Right now, I think I might have found the best sounding amplifier for martin logan. I have gone through approximately 34-36 amplifiers in the past 12 months. Some of these are:

Bryston ST, SST, SST2 series

With all that said, the amplifiers I mentioned above are the ones that in my opinion are worth mentioning. To make a long story short, there is NO 5 CHANNEL POWER AMP that sounds as good as a 3ch and 2ch amplifier combination. i have done both experiments and the truth is that YOU DO lose details and more channel separation,etc when you select a 5 channel power amplifier of any manufacturer.
My recollection of what each amp sounded like is as follows:

ATI SIGNATURE SERIES 6005 (great power and amazing soundstage. Very low noise floor, BUT this amplifiers NEEDS TO BE cranked up in order to fully enjoy it. If you like listening at low volume levels or somewhat moderate, you are wasting your time here. This amp won't sound any different than many other brands out there at this volume. The bass is great, good highs although they are a bit bright for my taste)

NAD M25 (very smooth, powerful, but somewhat thin sounding as far as bass goes)
Bryston sst2(detailed, good soundstage, good power, but can be a little forward with certain speakers which could make them ear fatiguing at loud volumes)

Krell (fast sounding, nice bass attack, nice highs, but some detail does get lost with certain speakers)

rotel (good amp for the money, but too bright in my opinion)

cary audio (good sound overall, very musical, but it didn't have enough oomph)

parasound halo (good detail, great bass, but it still holds back some background detail that i can hear in others)

lexicon (very laid back and smooth. huge power, but if you like more detail or crisper highs, this amp will disappoint you)

McIntosh mc205 (probably the worst multichannel amp given its price point. it was too thin sounding, had detail but lacked bass.

butler audio (good amplifier. very warm and smooth sweet sounding. i think for the money, this is a better amp than the parasound a51)

pass labs (very VERY musical with excellent bass control. You can listen to this for hours and hours without getting ear fatigue. however, it DOES NOT do well in home theater applications if all you have is a 2 channel set up for movies. The midrange gets somewhat "muddy" or very weak sounding that you find yourself trying to turn it up.

classe audio (best amplifier for multi channel applications. i simply COULDNT FIND a better multi channel amplifier PERIOD. IT has amazing smoothness, amazing power and good bass control although i would say krell has much better bass control)

This brings me to the mark levinsons h series (532h and 533h to be specific). I have done EXTENSIVE listening with them for the past 2 weeks and i will say that NO OTHER amplifier gave me a better blend of everything as these amps did. They have EVERYTHING from top to bottom. Granted, i still think krell has better bass, BUT the highs and midrange smoothness are UNMATCHED. I really thought that i was going to simply try them and move on to the next amplifiers and i just couldn't. My mind was set that i was going to keep the classe audio, but the levinsons just did everything better. I can't really say anything bad about it other than perhaps some of you might need MORE POWER in a larger room. They are THE ONLY amplifier that i can listen to at low volumes and HEAR everything and each detail. It doesn't lose a thing even at low volume. I have never experienced this before. Very 3 dimensional. Is it worth the retail price? no it is not, BUT if you find it at good deal, make no mistake this H SERIES will beat whatever you have in your set up right now UNLESS you are talking crazy ultra high end units out there. If you can pick up one of these puppies in good shape for under 5,000, i don't think you can do better. It will BEAT any 2 channel amp that you can think of for under 10,000 in my opinion. The only other amp i can't speak of is the plinius sa 103, but if i do find it at a good price, i might have a review for it.
Some of you might be in the quest for a good 2 channel or maybe a 5 channel amplifier in which i recommend what i have which is the 533h and 532h. i am willing to put up money on the table that this 2 amplifiers would be ANY 5 channel amplifiers out there REGARDLESS of the price period. Everything comes to life with these. I can say that if you have money to spend and are ACTUALLY wanting to HEAR an improvement in sound over what you have, DO NOT overlook the h series amplifiers from levinson. It will blow your mind.
I've had a Levinson #532H for several years now, I love it as well.
i am actually in the process of doing a a/b comparison of the 532h vs the plinius sa 103. It should be one interesting one!
Sounds good! I had a bad experience with Levinson many years ago, so I'm a bit leery to try it again. But, I did hear it at CES in the Harman room driving JBLs, and I thought it was pretty good. Better than what I remember...

Hi Whitecamaross
The Montis are a very heavy load, with low impedances and very high - phase angles, you need an amp that can deliver good current when asked without strain.
This means an amp that can keep near doubling it's wattage from 8ohms to 4ohms to 2ohms
One amp/s that I can think of that's not on your list is the mono block Parasound JC1's and they have the added benefit of a high bias class A switch on the back when your seriously listening. And you can switch it off when just using it for background music.

Cheers George
Interesting to read you heard a difference between the Levinson 500H series and the ATI 6000 series. I looked at their amplifier modules (both manufacutred by ATI) and they look 99% identical (different colour of circuit board and some tiny wiring differences) with the ATI ones having slightly more capacitance (18 vs 14 capacitors).
It is a shocking similarity:
ATI 6000 platine excluding heatsink

Mark LEvinson 531H module:

The 6000 series is also much newer then the 500H series which is a bit older now. I would not be surprised if ATI pretty much based their design on the Levinson 500H design.

That said the manufactures must "voice" their amplifieres differently if you hear a difference.
YES, the levinsons are MUCH better at ANY volume level. The ati needs to be cranked up in order to enjoy it. It doesn't shine during low volume listening sessions.
I doubt your claim given the spec and construction of the ati vs levinson.
Nevertheless due to your raving reviewI will get them both for comparison at home. I hope i am not waisting my time. The levinson looks like a waste of money given identical or actually worse specification.
I HAVE OWNED BOTH. i don't care what the specs say. The mark levinson is voice VERY differently. They sound waaaaay better regardless of the volume level. i speak from my own personal experience and not from some lame magazine review that gets paid to say something good about a certai product. Most people here go by what others say, but i have owned both so i am speaking from first hand experience. The ati signature is VERY BRIGHT sounding and the guy who i sold it to also decided to sell it after owning it for only one month. He went to parasound because he couldn't tame the high frequencies in the ati. I don't care how you present it, the ati isn't the same. Mark levinson simply ROCKS with these new H series and they are extremely reliable.
Whitecam, when I was looking for an amp for my paradigm Signature S6 v2 speakers, I tried Emotiva which was way too bright. Talking to a co-worker, he recommended Mark Levinson with Martin logans. As I already had the $6000 speakers from Paradigm, I kept researching and ended up with Parasound. Your findings mirror mine with the Halo gear, a little warmer but without every last detail. This works perfect with Paradigm Sigs and I've been able to tune the system one way or the other with cables.
I own the martin logan montis and the mark levinson sounds BEAUTIFUL with the electrostatics. I don't even have a real processor yet the amplifiers sound amazing regardless of the volume level. I also think parasound halo is excellent with detail without being too forward. The ATI is forward sounding and will demand a warm sounding processor like the classe SSP. Marantz and ati DON'T GO well together. I prefer to have amplifiers that give me detail without causing fatigue after hours of listening. i love my levinsons and i had heard the entire bad rap sheet that levinson gets due to their high repair costs etc, but the H series is THE MOST RELIABLE amplifiers from mark levinson.
Don't listen to your local dealer trying to tell you the ATI is just a mark levinson, etc. IT IS NOT!. The design might be similar, but the levinsons have more detail and are smoother. i feel they are between pass labs and krell as far as detail. Not too bright and not too laid back.
Well I will demo myself. I can demo quite a couple of the amps you mentioned without needing to buy any of them so I can do an unbiased demo (owning one creates usually bias due to sunk cost). (other then being biased against expensive amps that provide no audible upside).

I arranged a demo of the ATI in the 7 channel config vs. Mark Levinson 532H vs the new Krell Duo (vs potentially Classe-CA2300).
For ultimate comparison I will compare all of those to my current Gryphon Antileon Signature (pure class A) stereo amp which cost 3x as much as any of these so there will be a proper comparison opportunity (i actually want one of those amps to sound better or equal to the gryphon...) ;-)

Demo will be with my Classe SSP800 as processor/dac and wilson benesch (Chimera) speakers which use a silk dome tweeter so both front and speakers are not on the bright/edgy side such as Marantz or beryllium tweeters.
ATI oems for Levinson so I am not surprised that the innards are almost the same.
yes, ATI builds for levinson because they had to go to a reliable manufacturer and not keep making the same mistakes of building unreliable units since that was clearly hurting them. I can tell you that these amps sound VERY DIFFERENT. I do find it funny how the vast majority think that because ati makes it, then both amps must sound the same. However, what people DON'T realize is that they are voiced VERY VERY differently. The ati is more forward as I stated above so maybe it would benefit from a laid back preamplifier. I would take the classe 5200 or 5300 ANY DAY over the ati. Why? I am not a fan of bright or forward sounding amps. The most I can handle are the high frequencies from Krell. That is as far as I want to go. The BEST multichannel amp I have heard is the classe HANDS DOWN. However, a 3ch levinson along with a 2 channel would beat a classe 5200 or 5300. I have done this comparison.