@nymarty Congrats and welcome to audio Nirvana. Amazing preamp you will not be disappointed. Here’s another thread you should read and follow. Contact @jslateiv he is Supatek’s official repair tech for your questions. He is a wealth of information and very helpful. I use RCA’s and have a sub connected with no noise. The bass was so strong I had to add a volume control between the pre outputs and the sub line inputs.
https://forum.audiogon.com/discussions/supratek-owners-thread