IMO Mini3 has a slightly grainy top end and a slightly exaggerated mid. As a whole a bit aggressive. I don't think it has anything to do with design or passive parts. Since amb shows square waves and RMAA tests, we can be absolutely sure the amp has a flawless design and layout. It's just the way AD8397 sounds.
The placebo effect is very strong when you modify stuff yourself, and especially if you pay serious money for the parts, and even more if the parts look nice. In this kind of topology with an active ground channel, and the opamps running at quite high bias current, capacitors have very little impact on sound quality.
When it comes to resistor "sound" some claim there's a difference. If there is, it's very minor. IMO it's the active parts that really make a difference, like opamps and transistors, and capacitors if they're in the audio path.
