There is some interpretation to the power ratings and how to define "max power". Typically this is when the distortion level at some high power level increases to some predefined level such as 1 percent. 1 percent is the same as -40dB. When you look at the distortion measurement from the review below (continued):
... you can see that -40dB is reached for a power level of about 200 W. The distortion starts to climb at the lower power level of 156W but there the distortion level is only circa -87dB or 0.005%. Some amplifers NEVER reach that for any power level, and I have wondered why this is assigned the "max power" level by Amir in other reviews as well.
There is an old GFA-555 II review with good measurements you can compare to here:
There is a lot of good info contained therein. A plot of distortion vs power shows that the distortion level of the Adcom stays pretty low and constant at about 0.0005% at below 1W to about 0.0015% above 1W until turning up at 100W. This was when "new", and this is getting long in the tooth at this point and some component aging has likely occurred. Your amp may be performing much worse than this but you wouldn't know unless there was a major failure somewhere. The ear is just not all that sensitive to distortion.
What the Adcom amplifier (if it is actually performing up to original specs, likely not due to age and some PS cap degradation) offers is some headroom above the max power spec, for brief transients and with elevated distortion. The review lists that a power level of 265W was obtained with 0.68% THD (still not at 1 percent!).
IMHO overall the Buckeye amp's performance will be superior in terms of distortion at pretty much any power level up to about 100W, is brand new, running at spec (minus the current bug that is being worked out), and has a lower noise floor. The GFA-555 II is a very well regarded amp, but at this time you would be getting better performance out of the new Buckeye amp. I do not think you will miss the last 50 Watts or so, that is only 1dB or so difference at 200W and unless you are listening so that your ears bleed you will never reach these power levels except on transients.
It's possible to get the Adcom completely overhauled, with PS caps checked and lots of other components replaced and updated. This is another option you might consider. It's a very good amp when working well and up to spec.
The other option that I have to bring up, and one that might make a much bigger difference overall, is to upgrade those M&K speakers. I auditioned them IIRC in the late 1990s against a pair of Snell K-IIs that I owned and I was shocked how much worse the M&Ks sounded at the time. If you want to upgrade your "sound" you might start there and not with the amplifier. Lots of good commercial speakers under $2k these days. Just my unsolicited 2 cents. Take it or leave it.
