A small annoyance while biamping

I'd say pre-amp is outputting a bit of signal with volume down.Speakers can only play when sent voltage.

Try swapping the left and right speaker connections. That will show whether it's a speaker problem or an amp problem.

You could also try swapping L-R connections between pre and power amps and see if the problem changes channel. This would tell you that perhaps one power amp was the problem.

My guess is that the volume pot on the CJ preamp is slightly out of balance at very low volumes, such that one channel is not completely attenuated. This is a common problem with potentiometers, and there's not much that can be done.