Stand off means that to sound their best, they should be placed a certain distance from walls. They are just guidelines though, the Hsu speakers will still sound good if you don't have them placed in that exact ratio from the walls. But what you don't want to do is mount them directly against a wall as they are rear-ported, and the ports need room to breath.
The SVS speakers don't have any ports and can be mounted directly against a wall. And yes, the only difference between the SCS and SBS is the extra woofer, this gives the SCS a bit more power. In sensitivity though, it still does not match the HB-1's. Like the other poster said, I would stay away from the SBS speakers in a large room. I don't know how the SCS will handle large spaces, but the Hsu speakers are fairly powerful and will handle it fine.
Some other speakers in their league are the Ascend Acoustics CBM-170's, the Infinity Primus P162's, and the Behringer 2030p's and 2031p's. I think the Hsu's might be the best at coping with larger rooms between them all, due to the horn-loaded tweeter, although I have not heard the Ascend speakers (but would very much like too).
