Well, that's nice to know. I tried Burson V5i-D op-amps without any issues, sounded great. Of course, can't slide the boards back in due to height clearance which you already resolved. I also picked up a couple Analog Devices AD827SQ per a recommendation by our friend
@WoodyLuvr, but they did not work at all. Those AD827SQ had a loud hiss. That's actually why I measured the op-amp supply rails because I could not figure out the cause of the loud hiss. Since we don't have a schematic, the only thing I could think of is that the op-amp circuit is optimized for MUSES02, though the AD827SQ should be compatible and has the same pinout.
I did try NE5532 and Burson 5i-D which both worked fine, but those AD827SQ did not. Having said that, the AD827SQ did work in my Little Bear B4-X which has a higher + / - supply rail then the Tap-1. It could also be that I got counterfeit AD827SQ op-amps since I got them on ebay. Reliable sources like mouser or digikey don't have them in stock and I'm not even sure if Analog Devices still manufactures the AD827SQ.