Based on another thread (thanks again, Stan), I learnt that I can connect my turntable, have Aux l+r for bass output, AND still use analogue bypass mode. The change in audio quality is not trivial, my LPs are getting a spin even as I write this...
I was previously using stereo mode as I thought bass redirection to Aux required it. As a caution to anyone using stereo mode for a stereo analogue source, don't do it.