Rebooting this..to the OP, did you solve this? Did you test this using headphones too?
I've experienced something similar using the P5 Preamp with active speakers. Noticed unbalanced sound in different pairs of headphones (but assuming that's a P5 headphone amp issue).
I've experienced something similar using the P5 Preamp with active speakers. Noticed unbalanced sound in different pairs of headphones (but assuming that's a P5 headphone amp issue).