MAC fans - MC206 harsh?

I was just over a friends house. He has been complaining for some time that his Macintosh MC206 multichannel amp is harsh and bright. He Has B&W802N's and he is bi-amping each speaker using two channels of the MC206 per speaker (the other two channels do his matching center channel). Cable's and IC's are top to the line straightwire. Pre-amp is a Lexicon MC12(?). Sources are Pioneer CLD-95 laserdisc and Pionner DVD09 DVD player.

First of all, the CLD-95 sounds better then the DVD09 in analog. Now that we got that out of the way lets move on to the real problem. When he turns up the volume the system just looses it. I mean, the sound gets harsh and the music looses all the detail and nauce. Now, I don't mean 'piss of the neighbors' loud; I mean moderately loud but you can still talk over it with a little effort. At low volume levels, like background music, the system sounds pretty good (not actually my cup of tea...). We played around with placement of the speakers and room treatments, but nothing really helped.

So, any suggestions or insight?

PS-all listening done in two channel.
the preamp in his system is most likely setting the 'tone' of the playback. mac amps throughout the line have a darker, warmer tonal quality than most ss components. they are however, like all power amps, influenced by. the preamp,which in your friends system is really made for movies for than music
I have an MC206 and I can't say that I find it harsh and bright. I'm using modified Klipschorns for my mains and center. Stock Klipschorn bass horns with the K33E woofer. Altec 290-16K midrange drivers with an Altec 311-90 horn. JBL-2404H tweeters, all with a custom network (crossover). If this amp was harsh and bright I think I would be hearing it with this speakers.
hom many hours on the amp?

I'm running mine through Mx-134 and old pair of Monitor Audio MA1600 Golds --not a fair comparison with your B&W's but I hear no harshness at all. Is Power sentry kicking in prematurely?