Replace just the Main power fuse first. That will answer your question. If you can't hear the differences in nuance at that point... Then again: It sounds like you were able to discern the differences with a power cord swap(if I'm reading your post correctly). NO ONE knows what actually happens between electrons and metal crystals at the quantum level: So- OPINIONS BE DAMNED!! What those of us that CAN hear, DO hear, is all that matters.
do fancy fuses help?
wondering if there is any consensus whether expensive fuses, e.g. hi-fi tuning ceramic, really do help and are worth the money. is it like power cord voodoo (that is, they can make an audible improvement, logic be damned), or is there a theory behind why they might improve things? My amp uses 6 fuses, so a $250 experiment is only "cheap" upgrade by our insane audiophile standards.