This I have been experimenting - call it a hunch - on the effects of bypassing electrolytic capcitors (Nichicon FW and KW) with 0.1 uF TDK ceramics (Mouser 810-FK28X7S2A104K) with the diamond buffer circuit used in both my B-board preamp
and Sapphire headphone amplifier
This being a mod, I had to solder the caps to the underside of the boards, attached to the leads of the Nichicon 100uF electrolyic capacitors.
I used four ceramics per channel, one per active device in the diamond buffer if you like.
I did several other changes on the B-board at the same time, so it wasn't obvious until I modded the Sapphire in the same way what was the result of the bypassing. Anyway, with both the improvement was immediate and dramatic: any sense of "transistor-like" treble glare is completely quenched. The whole top end takes a step backwards, not in extension, but in prominence.
Less audiophile detail, more swinging mojo.