OK...for one thing, Klipsch and B&W are completely different in voice matching. I own B&W 600 series speakers & have a friend with all Klipsch in his HT setup...totally different sound! Absolutely stay within the same brand of speaker if at all possible. If you can stay in the same series, even better.
Yes i know that your surround channels are not AS important as your front sound stage but you do want a seamless transition from front to back as previously recommended. If you are happy with the 700 series then dont get a different brand for your rears, it wont sound right.
I hope you find what you are looking for in end buddy!!