Amp newbie? Adcom GFA-555 vs Mcintosh 2505

Hi I'm definitely a newbie, and already know my initial choices in starting my first adult sound system will make experienced folks around here cringe...but I'm wondering if I might still garnish a bit of insight to help reduce additional "bad" choices or steepen the learning curve just a bit.

From the beginning; I went and auditioned speakers at Best Buy, and of course fell in love with Martin Logans...and decided to order a pair of Magnepan MMGs (not a bad start right?). Did some research and bought a HK3490, maybe not the wisest choice...kind of wish I had started with separates...but it should be able to handle the MMGs...I know I amjumping the gun a little because I have not even heard this combo due to some shipping issues with Magnepan...but my question is this...I'm thinking I can use the HK3490 as my preamp and add a separate amp?

And the real question how do you compare amps...I am looking at a few intro. affordability choices like the Adcom GFA-555 rated at 200w/channel vs. the Mcintosh 2505 rated at 50w/channel...but I'm under the belief it's not just the watts, but the amps that are driving them...otherwise my HK3490 at 120w/channel should have the juice to power the how do I know which will deliver a better sound for the buck...and more many watts do I really need?
I'll take a shot here and suppose the Maggies are monitors, not panels, right? Also that their impedance is above 4 ohms, right?

If so, then perhaps first things first... connect them (when they arrive) to the HK.... and go from there.

True, there are watts and then tere are WATTS, but the speakers needs for power and control as well as the room they're in pretty much determine what size amp should push them... your preffs will deteremine which size amps 'voice' will do it for you.

If you have preamp outputs, sure, another amp can be added/used instead of the rec's amps. As much as I'd probably prefer the Mac over the Adcom, the 50wpc bothers me a lot... but does depend on how much volume you want to get out of the speakers... and that's where your preffs and the room size comes into play.

I think the bulk of SS amps range around the 150 - 250wpc mark. Almost every amp maker out there makes one in that area. having one on hnad which has the numbers allows you more flexibility with speakers... and usually, only less power damges them, not more power.

Take you thesis a step further... a Krell KSA 50 OR LEVINSON ON THE SAME ORDER, SHOULD BE STILL MORE ADEPT THAN THE MAC...

Try the HK and go from there. Odyssey makes some great sounding amps and are routinely traded here for reasonable rates.
You want to look at the specs for the rating at 4 ohms. This will give a clue as to the size of the power supply. If the rating from 8 ohms to 4 ohms doubles then you have very high current which what Magnepans need.
Based on my preferences with the benefit of doubt to system synergy I would say Mac...mac...mac.

You can visit Audiokarma Mac forum to get a better idea on this particular amp. Good luck on your search & hope the learning cuve would be steep! Cheers.
I think your HK will be fine for pushing the MMG, I would see how you like it before pulling the trigger on a new amp. Magnepans are actually an easy load for amplifiers due to the fact the that are purely resistive, none of the wild impedance curves typical of box speakers. If it turns out you really like planars then you will probably upgrade to the 1.6s at some point, that is when you will really need to upgrade your amp.
The mangepans are planars with a nominal 4 ohm load.
Wind - I'm a relative newbie driving MMGs with a 200w (360w into 4 ohms) ss power amp. I think mine (a B&K) does the job well (smooth, warm sound) but haven't done the comparisons to have an informed opinion. I took a similar route as you with preamps and began by using the preamp output of a Rotel integrated. I am happy to have an e-mail discussion about this since we are in a similar boat, but 2 comments: 1) the preamp selection is very, very important; 2) MMGs are great. You are going to love them long time.
Thank all for your responses so far as some additional concerns... Drumhead- HK3490 is rated at 120 wpc at 8 ohms, and only 150 wpc at 4 ohms, this was my first concern (although their literature says it is stable at 4 ohms)...and Bwp- yes, I am already eyeing some of the used 1.6's around here...and yes the final concern...I have a slightly addictive personality and I see potential problems down the there an audiophile 12 step program in the LA area by any chance? ;-) I might need an intervention!

Power ratings of receivers won’t usually double when imp is halved… as some other amps will. That doubling down aspect is no reason to reject an amp either.

RE Audio 12 step

First things first…. Place a greater priority on what you have, rather than what you desire. It’ll always work itself out. Always. One day at a time.

Turning off the personal confuser and listening to your system will help immensely too.
I wouldn't push the volume too much on the HK. It only consumes 310 watts max.That sounds like they may be giving it a higher power rating than it can really give out.Be careful until you get a quality power amp capable of driving 4 ohm loads all the time.Maybe start a new thread asking for the best sounding lower price amp to buy for the Magnepans.Stating a price limit will help too.