Whoa, tough call. IMO an HT system with phantom center is not going to sound any different from hooking your DVD player into the 3480. Remember that "phantom center" is just mixing the center content into the two mains -- and that happens on the stereo outputs of your DVD player anyways.
My first thought is to keep things pure. If you want a stereo system, get the 3480 and M60s and forget about the sub. The M60s have all the bass you need for music, they just don't do explosions, dinosaur footsteps and atmospheric bass drones all that well.
If you think your stereo is going to get rolled into the home theater in the future, get an AV receiver today plus the M60s. Get a sub only if you have budget for the big honkin' sub you're going to want for the HT in the future.
If you're pretty sure the stereo will stay separate, go for the 3480 and forget the sub for now.
That's my 2 cents anyways
