NAD vs. Adcom

thinking to upgrade power amp to make B&W dm604 s3s sing. any thoughts on NAD s200 vs Adcom gfa 555II or GFA 5500? currently biamped with NAD c325bee driving mids and highs and Adcom gfa535II driving bass {using preamp section of c325bee}
Depending on budget, I would look at something other than the Adcom amp.....besides it being an old amp, its not very musical sounding at all.
I agree that Adcom products are not very musical. However, many people seem to like to 555 II. What is your budget? Maybe you could get into a McCormack amp-say the DNA .5. That is a very good amp. If not, try a B&K ST-140. Very musical, 120 watts per channel, and used its about $200. Enjoy.
This looks like a very good deal and a step up.
I owned (4) GFA555IIs.
I owned (2) GFA 5500s.
The 555s are & were great for sub amps, but forward (bright) on my Magnepan 3.3Rs.
The 5500 is current, and sounds much more musical, to me.
I only sold both to go to Fully Balanced amps.
Ive own 3 Adcom amps 5802 ,555 ,2535 . If you have speakers that are bright go with the 5500 . Dull speakers would benefit from the 555ii . Mosfets almost always sound better than bi-polar in my opinion.
No doubt, some speakers are inefficent and thus require some 'ooomph' to make them sing. However, you may find that a good separate pre-amp may make more of an improvement dollar for dollar than upgrading your amp, especially since you are bi-amping.

Interesting that no one has commented about your bi-amping with different amps. I've always heard that it is recommened to use identical amps when bi-amping. I wonder if using identical amps would improve the 'singing' ability of your speakers?
Don't over look B&K amps. I recently heard one and was impressed given money spent.
No comments on the possibility of the NAD Silverline S200 amp [probably in conjunction with the S100 preamp]?
I'd guess the bi-amping with such dissimilar amps may be the 'problem'.

Almost any single more powerful amp will help. A good integrated which can handle the B&W load, not just impedance but phase angle as well, is recommended.

Maybe a NAD in the 37x series? That is, if you like the NAD house sound?

One of the M series integrates would work like mad, but the cost may be a little brisk.

BiPolar? MOSFET? Good bad exist with either device type. If it works well with your speakers, don't let either deter you.