Alex,
(sorry for the later reply)
I’m glad that helped with the power supply.
It sounds like something is wrong with you effects loop (or Quaverato). There should not be a volume drop at all. The input impedance of the Quaverato is 1M ohm and that is overly sufficient for any line level output. Have you used this line out before with other pedals? Does the Quaverato work fine when a guitar is plugged into its input while its output is plugged into the guitar amp input jack? Are the cables known to be all good? I don’t know what else it could be. I’m sorry, I hope you are able to figure this out.
-Brach