Please help me with my surround setup.

It would definitely be better to use BP2X as side surrounds. The drivers in the BP2X would be perfectly matched to the SM350. Use the SM350s as your front mains. If you have another pair of SM350s, use those for your rear surround. You could still use the BP1.2X for the rear also, but they do have 4 1/2" drivers in them, whereas all your other speakers have 5 1/4" drivers. What are you using for your center channel?

I do know of someone who used BPVXs for his mains with very good results, but that was just a temporary solution till he received his real mains. Are you unhappy with the SM350s' performance in the front L&R position? Def Techs' BP2X, BPX, and BPVX perform amazingly well in the position they were design for... surrounds. Especially side surround. Of course, you can use them in other positions with varying results, but why. What are you using for the center channel ???

Using a SM350 for a center would work very well and you would have a great front sound stage that is perfectly matched. A pair of BPXs for 300 bucks??? If they are cosmetically fine and in proper working order, then those BPXs might look better on my walls . It's too hard to tell how the BP surrounds would sound as front mains. Even if you waited a month until someone who is doing that, posted a reply, saying how much they liked it, you may end up... not liking it after you have bought them. Even if they sounded okay in the store with that setup, that may not be the case at home. If there is a good return policy, then that would give you an opportunity to try it out. I will add, it is such a great deal, I wouldn't return them anyway. You could always sell a pair of BP1.2Xs to free up some more funds.

Just one SM350 would work fine for the center. I've never listened to the RVSSs before, so I couldn't comment. You could use SM350s for mains and upgrade just the center channel for now to the PC2000, or CLR2002.