New to the game. Please help with set up.

I have been using a mixed marriage of drivers for years, with ok results. As long as the speakers are somewhat similar in timbre, they will do just fine. Level matching is not a problem with multi-channel, so sensitvity isn't really an issue. I am more into 2 channel, but when playing M/C recordings, I get most of the desired results.
As previously stated, it will cause no harm, and it might surprise you with how good it sounds. Have fun with it, if you like it, great, if not, you are free to try anything you can afford later.

Enjoy,
Dan

Hi Michael:

My comments are should be considered supplementary vs. contrary to the good guidance posted so far. Let me suggest that you look at this as an opportunity to build up a system over time.

Given the 805s are likely the strong player (I have to cop to a pro-B&W bias) in your current setup, you could build from that foundation one piece at a time as budget allows.

Were in in your shoes, I'd follow CKoffends advice and get that matching center channel in place first. Either another 805 or an HTM 2 would be a good fit. You could go bigger into the HTM 1 since the center channel does the lion's share of the work on theater playback.

Given three B&Ws across the front, you have enough of the sibs for both rear and side surrounds (plus a spare), assuming your Pioneer can handle that.

After the matching B&W Center, I would then focus on outboard amplification for at least the Left/Right front channels. Were it me, I'd go for a high quality three channel amp to power all the front speakers. All of the B&Ws are worthy of good amplification and the biggest benefits will probably come in the area of bass control.

That would present a pretty satisfying system and assuming a good amp was chosen, you should get many years of satisfaction and service.

From there, I'd work my way up to a high quality H/T processor (preferably one with two-channel analog bypass for music only).

Then a sub that's able to go pretty deep and pressurize your good sized room.

I also agree with the postings that the rear surrounds are far less critical for timbre matching so they'd be the last thing on my upgrade wish list. I hope this is helpful advice!