Solved: For anyone finding this in the future:

1. it is important that both the rca jack and the pot, as well as the tube sockets are mounted appropriately. Otherwise they are mirror imaged - this also becomes very important to verify (and use your cap discharge tool) as when they are in reversed, the caps will not discharge as expected at power off.

2. If you are making the zkit2, and your high power side tests correctly but your audio side is dead, double-check the connection on your jumper and that you've chosen the correct jumper for your input tube.

Otherwise an amazing experience building can't wait to do the next two!