AirKuhl,
You have stated that multi-channel music is the first priority. Therefore 4 matched speakers plus a center speaker that can be matched as closely as possible to the 4, and fit horizontally in the space below the TV is indicated.
1. Based on the available floor space on either side of the entertainment center and the budget, the HT3s meet neither criteria.
2. The SongTowers or the HT1-TL or the HT2-TL are a better fit for both the space limitations and the budget.
3. With the dimensions of available space below the TV in hand, it is very likely that Jim can come up with a configuration of a "matching" horizontal center speaker that closely matches the voicing of the other speakers you choose.
4. The speakers mentioned in #2 are also a bit more efficient than the HT3s, and won't place as great a load on the amplifier. Whether you prefer the simplicity of a receiver such as the Arcam AVR600, or want to go the separates route with a surround processor and multi-channel amplifier, is up to you. Either would do the job, but I don't see a processor like the Anthem DV2 that alone costs $6K as being part of this equation.
5. There are quite a few subwoofers that would work, but whether you want to use the entertainment cabinet space to house the subwoofer or have it (them) out in the room, I think one that has built-in room correction would be advantageous, unless you want to use an external room correction unit, and have yet another component. I am not familiar enough with the current processors and receivers to know how good their room correction is as applied to subwoofers, so if someone else does, please add your input.
Steve