I'm also in this dilema. I have the 568.2MM/598 combo and a Bryston BP25 with the MM phono stage. For sub management, I just found it easier to just buy a second sub. I keep my HGS12II tuned and dialed in with my B&W Nautilus 804s. That way I can have the sub anytime to help the 804s....music...movie...whatever. I picked up a HGS15II as my LFE sub to enhance movies. So that's how I got around the issue. I wish Bryston would look into a unity gain for the BP25 but alas they don't have any interest in doing the mod. So I'm stuck with trying my best to calibrate the mains referenced with the BP25 volume set in the 12 o'clock position.