Adcom GFA 535II or 545II/suggestions

Presently running the 535 II is there a noticible difference if I upgrade to 545II @ 100 wpc vs. 60wpc? Any other suggestions in the 200.00 used range? Will be powering Monitor Audio S8's Thanks for the input..
You'll not notice any difference to speak of. The difference in output volume is less than 3db. One db being barely audible. Every time you double the power you have an increase in volume of 3db so there would really be no benefit. I'd wait til I could save at least another hundred dollars for a 150 or 200 wpc amp.
If you could spend a little bit more, go for Adcom GFA 555 which is a lot better than the other two.
I owned a GFA555 for several years and it was OK. I traded down to a GFA 545II and recently swapped it out with a B&K Reference 4420. Huge differnece in sound quality on the B&W. Much better midrange, vocals crisper, bass deeper and more refined. The B&K wasn't that much more expensive either, but I was shocked at how much better performing the amp was. You can find them here for $550. I have also had good luck with a C-J MF-2200, and there is a MF-2100 up for sale right now at $525 if you only need 100wpc. Again, a much better choice than the Adcom, IMO. I would look for something a little higher-end if you can at all afford it-just my $.02.
I had a 555 briefly and thought it was mediocre. However i have a 545 mk2 right now that is WAY better - I am impressed with this amp for the price. It isn't quite as good as my McIntosh but the Mc is a lot more expensive. BTW, I am selling my 545 very soon on Audiogon. Email me if you are interested.

I haven't been impressed with B&K before but then again, I haven't had any of their equip in my own system.
Elsewhere, Adcom amps of that series have been said to be better the lower the power, as long as your speakers are getting the juice they need. In other words, as you get more watts you pay for them in sound quality. So it is possible that you would notice a difference if you moved from the 535 to the 545 or the 555, but you might not like it.

Aball's experience would seem to confirm the idea that lower-powered amps in this series sound better. Of course, he is planning to sell a 545... ;o)

My best 2 cents is that Warnerwh and Chiho have very good advice. Upgrades are expensive--less if you are doing it on the 'gon, perhaps, but chancier too, since here you can't listen before you buy. It makes sense to take the biggest possible step each time.

One good SS amp I have owned is the Sima Celeste W-4070SE, a nominal 70-watter that sounds like a lot more. Bigger models in the same series were the W-4150SE and W-4250SE. Simaudio no longer makes them but you can find info on their site, at this address:
(Sorry this is not clickable--I tried but the edit post page won't do it.)

These amps obey the Adcom rule--as they get bigger, they get just a little less lively--but any of them would be a real upgrade for you.

Then there are tubes, of course...