"Much" better when moving from 125W to 200W is difficult to believe. When moving between good quality power amps, I expect changes to be incremental and subtle - if there is a really dramatic difference, I start looking for problems somewhere. The same should be true in your case. Adcom's amps are generally good, and you've already got a decent bit of power per channel. The extra headroom amounts to just a couple dB of output. And with speakers that are have a sensitivity of 90dB (according to a brochure I found at B&W's site for the DM603 s3), you would need to have it in a truly gigantic space to need more than 125W of power to get good results from those speakers.