do fancy fuses help?

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.

I started a thread on this question on the HIFICRITIC forum. Got some interesting answers, you might want to take a look.

For one of the more heated discussions on this topic you could check here. My opinion is damned.

Yes a fuse in the amp can be very helpful it saved a $3000 stereo Musical fidelity and some vintage stuff that couldc have caught fire and burned down the house the development town county and other parts of the state for want of a Nail. (In fond memory of rosanne rosannadana)

It can't hurt