Advice on rear surround speakers for 7.1

[capitan100]

Here is my current set-up in my family room.

A/V receiver- Sony V555ES 5.1 receiver
Sony DVP-S7700 DVD player
Sony SACD DVP-NC80V DVD player
Fronts - Polk RT2000i
Center - Polk CS400
Rears - Polk RT1000i
Subwoofer - a/d/s MS3/U

I just recently bought a Sony STR-DA7ES 7.1 receiver and I will be moving the V555ES up to my game room and hook up to my SDA 2B's. I am looking to get a set of rear surrounds to complete my 7.1 set-up. What pair of Polk speakers would best match my system?

f/x series Dipole/Bipole speakers? f/x 300 or f/x5 00
RT series floorstanders such as RT600, RT800 or another pair of RT1000i's? I do have one extra RT1000i, but not 2.
RT bookshelf speakers such as RT55 or RT35?

I also have up in my gameroom several pairs of bookshelf speakers. See my sig for types. Would using one of those bookshelf speakers as a temporary rear surround set-up sound bad or will the difference in timbre be negligible?

Thanks in advance.

BTW: I have not taken delivery on the DA7ES yet. I should get it by early next week. I bought it on the bay earlier this week. I can't wait to get it though.

[capitan100]

Would I be better served if I brought my SDA 2B's down into my home theater set-up?