bypassing the channel level controls?
I wouldn't. Have you tested your channels individually at your listening seat? I tested mine (250Hz; 500Hz; 1kHz) and discovered that the left channel was off by -3dB from the right. Why? Perhaps my room (asymmetrical, different openings left/right side)? Or tubes? Not sure, but am glad I discovered this. And glad I have the individual channel levels on my Mapletree Audio 2A SE Linestage to correct.
You may wish to check this out as well.