NAD vs. Adcom

This looks like a very good deal and a step up.
http://www.audiogon.com/cgi-bin/cls.pl?ampstran&1259646345&/Mccormack-Dna-0.5-classic-litt

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.