Like everyone else, I say go with the M60s. If you don't care about looks the Hsu STF-3 is a great deal. The VTF-3R sale is great.
If you want to match the look and color of your M60s, the EP350 is a good sub, too.
Regarding 9.1, personally I think that's overkill. I think 5.1 is adequate for virtually all surround music, and most home theater. I can see 7.1 if you're crazy about home theater, but not 9.1. There's definitely a diminishing law of returns. You may get a bigger bang-for-the-buck upgrading the sub or using M80s vs going to 7.1 or 9.1. Just my opinion.
