I have upvoted this for you. I agree that the granularity of this adjustment needs to be improved. I also believe that the auto-sync functionality for the bass management also needs correcting where the delay is measured from the MLP and not at the streamer itself. This hopefully can benefit the many users of the bass management in the WiiM. They also really ought to provide some options/control over the crossover slope steepness, even if filter type is not controllable.
As it stands, it (the integrated bass management) sucks, so I just use a miniDSP to handle it instead, but that's an expensive way to fix something that should be very simple to improve on the part of LinkPlay/WiiM.
-Ed