In general I'd recommend M22s, QS4s, and the STF-2 sub. You can get that for about $1k.
An alternate is moving the M3s to the side surround position, and getting M60s. But the M60s are pretty big so make sure you've got the space. Exceed your budget a little and add a Hsu STF-2, or keep your current sub and upgrade the center to a VP150. The VP150 is a lot bigger than the VP100 so check space carefully. If on top of your TV, make sure it can safely support the 17lb weight.
You already have a surround receiver now, stick with that. If you did 80% music, it might be worth upgrading to a receiver with Dolby PLII or HK Logic 7 to convert stereo to surround. However you are 80% HT, so this wouldn't apply as much. It's always tempting to upgrade the electronics, but you'll usually hear a much bigger difference by upgrading speakers.
I've had the STF-2 and a VTF-3, and the STF-2 was very impressive. If you upgrade your sub, I'd say the STF-2 is plenty for your situation.
