Connecting A & B to the same speaker sounds a bit alarming. I wouldnt do in myself. I agree with what sushi suggest just set it up in stereo mode. Yes the sub is on but you can easily turn it off and set the M3 back to large. Although a pain in the butt thats what I normally do when in music mode. Whats 20-25 seconds to change the setting to get a better sound.
One thing to note is that most bookshelves will gain better mids and highs (possibly more depth and stage) when you send your LF signals to a sub. Sending the LF to your sub makes you bookshelve easier to drive and give it a little more on mids and highs. I use my M22 & Mirage bi-polar sub and crossover at 65. Set my speakers to small. When I only use my M22 I set my speakers to Large.
Saturn
