Bryston vs Modwright?

I'm looking to replace my old power amp with a new one, in the $4500-5000 range; I'm running an ARC ref 5 SE that I got from a friend, and will be driving Dali helicon 400 mk 2s. I have been thinking solid state to complement the ref 5 SE, and have been exploring the Bryston 4bSST2 vs the Modwright kwa 100 SE. Anyone have experience with either or both of these amps?

I would highly recommend Bryston.  They are solid amps and the newer series sound wonderful!! 
Not sure your Dali's need such a big amp as the 4bSST2. Not heard either amp you mentioned but I'd recommend doing what you can to hear both amps in your system before making a purchase. Modwright and Audio Advisor on the Bryston will let you return their amp if you don't like them. I have had two ModWright preamps and love their product; very happy with my current LS 36.5, but I've not heard Dan's amps. I'd suggest a Pass amp and Reno HiFi can help you and they will send you something to demo too... see what they have used. I have a Pass amp and have no desire to ever change it out unless I move to a newer Pass.

One of my local shops had the original Dali 400 in for evaluation and I liked them but they passed on picking them up. I remember it was a fairly lively speaker and I would be concerned with the wrong amp it could sound bright; especially being a big SS amp. They really didn't have a amp in house that was up to the Dali's at the time, but I could tell it had potential. I felt a tube amp would be nice on them.

Before I picked up my Pass I had an ARC 100.2 and that was a wonderful amp and I've dragged home some newer ARC SS efforts and the hybrid they had a few years back and the 100 watt SS 100.2 was the better; dragged a couple Krell's home too and they were not to my liking. The 100.2 is a Very nice amp. If you can find one of these you will be amazed and if you don't like it they sell fast so you won't be stuck with it. Really is a wonderful amp but my Aerials needed more power so I went to a Pass which is a better amp and my speakers love it. 

If you can get a manufacture or retailer to send you a demo I'd do that first.
Good luck
Thanks so much for the advice! Yes, the Dali's are on the bright side, so wanted to find something to balance that. Will see if I can get some in-home demos.

Given your speakers don’t present an overly hard load, have a tendency toward brightness in the treble, and your budget I’d consider a Clayton Audio S40 Class A amp.  There's also a Plinius SA103 for sale in your price range if you feel you need more power.  Not sure the Bryston will do much to tame any perceived brightness you may have, so Modwright would probably be the better choice of the two. Best of luck.

Clayton Audio is a good recommendation, but I don't know if 50 wpc will be enough to drive those speakers.
I'd look into a Wells Audio Akasha, or a Innamorata if you can swing it.

I would go with the Modwright if only using your two choices. The Bryston would probably be too much yin with the ARC preamp and Dali's both being on the bright side of the fence. You need some yang to balance your sound.
Second the Plinius. Would also look at Audio Research Ref 75 with KT-150 tubes.
I have the Modwright KWA100SE driving Modwright LS100 preamp and formerly JM Reynaud Offrande Supremes and currently Daedalus Argos V2s. To my ears the KWA100SE is very pleasing sounding, not partial to one part of the spectrum, dynamic, non-fatiguing. I'll put the Argos aside as they are 98db efficient, the Offrandes are 92db and I never found having to crank the preamp above 10 in a 28x20x10 listening room. 
Meant to add, Dan Wright is very easy to speak to and willing to have a conversation. I'd give him a call and discuss your equipment, room, music tastes , etc. ; worth the call. 

One last point, my experience is that Modwright gear isn't partial to music genres. 
1+ facten

The Modwright amps and preamps are wonderful.  I've owned a couple of both.  Excellent build quality and sound.

Dan is great to work with, like others have stated.  

The Bryston is a sonic match for the ARC Ref5 SE pre-amp.
I have heard this combo (3B-ST and 4B-SST) on Wilson Audio speakers and Transparent Ref XL / OPUS cable systems. Excellent sound and presentation indeed!
Another recommendation for Modwright.  Very musical products and impeccable customer service!
Both good choices. Owned a 14BSST  and mated with an Audionote tube pre and it sounded great. Currently switch between solid state edge pre and allnic tube pre and love the match of tube pre with ss amp. I do not believe the issue of to much power is relevant-its more about quality and both are good choice-bryston 20yr warranty. Benefit of higher power is control over drivers particularly bass  Its not about the loudness. Also tube pre may help tame treble is speaker has a tendency towards brightness. Bryston has just launched a new amp replacing the sst models and suppose to offer even better performance. Another very good choice that a number of friends have owned is the moon amps-very good performance for $. Best wishes
I have an AR Ref 2 that I paired up with Odyssey Audio Kismet mono amps (in the Khartago case).. Great match up and 3D soundstage with Magnepan 3.6r’s and Vandersteen subs. Prior to the Kismet mono amps, I used an AR 100.2 (which is a terrific amp) for more than 10 years. That said, the Kismet mono’s were a significant step up in my system, particularly in the midrange... Just amazing
The thing which nobody seems to have mentioned yet is that Bryston has a virtually unheard of warranty on everything they sell.  Dig this...  It's a *20 year* full warranty that is transferrable.  In other words you can buy an 18 year old Bryston amp from someone you never met on EBay and Bryston will still service it under warranty. 

That does wonders for your re-sale value.  Today's $8,000 audio wonder is tomorrow's $4,000 white elephant.  With Bryston, you'll be able to much more easily resell it later.  Or if you like, you can buy an older Bryston amp and know that it's still under warranty today.
russbutton, I kinda agree with you on transferable warranty perk but who wants to buy 18 year old crap in times where everyone wants a piece of new technology.  

Gone are the days where you could get decent value for your used well kept gear.  Everyone out there wants to lowball on the gear that's already markdown at 50-60% off orginal retail. 

IMO, 20 year warranty is a mute point in today's tech world. 
Great point.  Odyssey Audio also offers a 20 yr transferable warranty.  Give Klaus at Odyssey a call.  He is a great guy that has been in business for years.  You'll get honest answers to your questions even if you do not buy his products.
I love the comment about "18 year old crap".    I'm not suggesting that anyone buy an 18 year old amp.  The point is that Bryston holds its value over time, much better than other product lines.  Look at all the high-ticket, 3 year old items on Audiogon that are selling for 50% of retail.  Expected resale is something worth considering.  That's one of the great advantages in buying a classic Mac tube amp.  You know you can always get your money back out of it whereas that wonderful new technology you so love will drop half its value in just a few years.
I was offered a Bryston 3BSST demo and took it home. It sounded good, so I talked to some guy at the factory, quizzed him for an hour, and it turned out he was the president! I bought the demo and ordered a 4BSST as well, to biamp a magnepan system, then a hybrid ESL system. 

Eventually did upgrade, but was always satisfied with the musicality. And there is value behind that 20 year warranty: they are hard to kill. Once I was moving an aluminum chassis around while I was playing music, and it shorted the terminals on the 4B. Arc welding. Huge spark. 4B shut right down, and I thought, "Wonder how much the banks of output transistors cost? Idiocy is not under warranty."

But, before I send it off for repair, I let it cool for 30 minutes and powered it up - no damage. I tested it harder - no damage. If robust matters to you, Bryston is a good choice.