The Hexfreds (or schottkys) didn't make a huge difference but they're easy to change and not expensive.
Replacing the psu caps is not possible as some of the uF values are very large with no ready higher-end substitutes. There's probably something else in your system worth throwing money at than this.
It might be possible to change some of the smaller hi & lo pass filter caps. That may not be worth it either (they're ok sounding). Send Chris J. the MOX link I sent you & see what he says.
Replacing the psu caps is not possible as some of the uF values are very large with no ready higher-end substitutes. There's probably something else in your system worth throwing money at than this.
It might be possible to change some of the smaller hi & lo pass filter caps. That may not be worth it either (they're ok sounding). Send Chris J. the MOX link I sent you & see what he says.