Ah, the old combined pickup conundrum. I even find combined, full on humbuckers are not as strident as a soloed ‘bucker (same for single coils). Once you start only using 1 coil of each humbucker, you’re compounding that volume drop even more. I’m sure that there is some kind of active circuit mod that would help with your dilemma, but I don’t have any details. Sorry.