The pic shows imbalanced bypassing.
Also what are you using on G_CH? Why I didn't solder R19 (wideband mode resistor for G_CH) is, I couldn't find merit for using it;(
And as you know, OPs on there should be higher output current type.
I don't always recommend 4ch architecture, so that produces DC, and I received massages from Japanese users who says 4ch architecture will give hiss.
BTW, I think stacked 634 won't go with the wideband mode (SW1 ON) when portable use, of course will get warmer than LT1210.
Wideband mode will make it effective with single 634P and 634U.
ad8397 is used in the ground channel.
My dad is the user of the amp and he think it sounds better with wide band width and 4ch. I can't have a proper test as all my iem is not with me till next week