I'm using a pair of SVS SB3000's with my M3 Sapphire's. Subs do reintroduce the issue that open baffle speakers solve over regular speakers - boxiness. That said, with a little tweaking, crossing the subs over at 55Hz, at -30db, with a 12db roll-off, they add a little weight that I find pleasant. For me they don't work well with one sub no matter where it's placed, but my room is far from ideal, with one side open to my kitchen. 1 sub just isn't ideal for stereo music and introduces more nodes and issues than it solves in my experience. But two, placed in opposite corners of the room, sounds decent. Opposite meaning, one sub placed against the wall behind my left main, and one in the opposite corner of the room behind me facing forward. I had them either side of my mains for a little while and it sounded a lot muddier than in opposing corners. I occasionally listen to the speakers without subs, and I miss the additional weight the subs provide. Since you have two of them in your other system, I'd recommend just trying them out as I described. Good luck!