May I ask what is being used as a preamp for this ?
I ask because should the preamp be the source of the SQ issues,,,swapping out amps may not "fix" things...
The Adcom GFA-535 Mk1 is definitely a GIGO sorta amp.
And generally speaking I usually dont care to pair my GFA-535 Mk1 w/Adcom preamps/pre-tuners if I can avoid doing so.
When (if) I do pair it with an Adcom preamp/pre-tuner I typically EQ mine to get the sound where I want it.
I do that as I dont necessarily care for the Adcom preamps tone controls,especially where they put the turnover Hz.
Typically they put their preamp's turnover frequencies @ very low Hz & very high Hz,and they leave the midrange unaltered.
Problem is if the source is a bit "shouty" -or- "bright" in the mids,there's no practical way to tame it down other than using an EQ.
And a lot of folks scoff at doing that sorta thing (using EQ's),so they try other things like changing out amps & speakers or such.
Anyhow just some food for thought.
Bret P.