All current multichannel receivers can function with a "Phantom" center as far as I know. In terms of how you will use it however, it depends. If you are talking about playing 5.1 music from DVDs, DTS CDs, SACD or DVD Audio discs, then the center is mastered as part of the mix and is intended to be used with a center speaker ideally. If you are talking about just CDs, LPs, etc... which are by design, stereo for the most part, then you could play back music in just 2.1 (or even 2.0). Have you heard a properly setup 5.1 system playing 5.1 music before? I personally don't like using the Phantom center feature, and it is a non-issue when playing back 2ch audio anyway.
First off, skip the Sony receiver, period, particularly if music is your goal. Fluance is a decent budget package to look at, so I think you are OK there, however I would mention your total budget as well so that we can perhaps help with some suggestions. I'd go with the PB-10 over the STF-2; the comparable HSU sub would be the VTF-2.
If quality of music is your main goal, I would spend more on a solid 2.1 setup than a lesser 5.1 setup because you can put more money into the main speakers instead of spreading it out over all of them. In the long run, you will spend more, but you will also end up with a better system IMHO.