Thor ta-1000 pre cap replacement -- advice

I am a new owner of a Thor TA-1000 preamp. What a fantastic piece of equipment. In my system it has a bit of a hard, tinny treble... just a bit. I want to try replacing caps with something warmer and wondered which caps should i replace? I see two small Hovland Musicaps and two small Multicaps. Then "beneath" the board (looking from the bottom of the unit here).... there are four big black caps... Solens i think. Which caps might be the place to start in order to warm the treble?

Before anyone asks, yes i am certain the treble issue stems from the thor. I have played w cables and tubes and will continue to do so but it needs something a bit more dramatic. I am willing to lose some detail to get rid of the issue.

Rest of system: sota star sapphire, grado reference sonata1, cec transport, audio note 3.1 sig dac, vtl mb-185 sig monoblocks, quad esl-63, vandersteen 2wq subs.

Thanks for thoughts!