I have the same speakers right now and I am looking for a sub as well. I talked to the tech guy at Magnepan the other day and he said anything clean and fast, he prefers 8 or 10", not any bigger. They seem to like Hsu's offerings, and he also mentioned that they have the Onix X-Sub set up with one of their displays and that he likes it. Right now, I am leaning towards that, although for my room size the guys at AV123 suggested that I run 2 of them, and that isn't in the budget right now, so I'm still hoping to pick up a used or b stock something. If not, I'll probably start out with one x-sub and see how it does, possibly upgrade or add on later. I have a friend that has 2 MMGWs in a 2 channel set up, and they sound great, but he has no sub, so we felt like they were really missing something. We picked up a Velodyne VRP-1000 the other night to try and it wasn't' as tight as we wanted, but it really filled out the sound of the Maggies. If you haven't' heard your speakers yet with a sub, you'll be really pleased with how they do when you add one. If you come across any deals on a piece that works well, let me know, I'm open to suggestions!