Thanks for all the replies.
Yes, that’s the preamp, and I would want to use the existing cutouts. And the objective is to improve the sound. I have an Elekit TU-8600s amp, and the Sunvalley preamp degrades the sound (particularly in the high frequencies). I’m trying some new tubes (switching out 12ax7 to 12au7) and want to also upgrade the controls and see what that all does.
I had a Hattor (Khozmo) passive preamp and a Tortuga tube preamp buffer and both the Hattor and Tortuga had problems from the start. I did, however, like the Khozmo duel mono attenuators.
I emailed with Gold Point about an input selector and a volume attenuator. I heard back from a guy named Arn and he also thought two mono attenuators (left where balance knob is and right where volume knob is) were the way to go. My hesitation with this is, one, my wife and kids use the system and it’s already complicated. And two, I worry I’ll have a hard time getting the balance even with two clockhand lines