I too have conflicting feelings when it comes to surrounds, although I personally prefer direct radiators and they're easier to resell should you desire to do so down the road.
As for what surrounds to get, if you answer "yes" to the following question, I think the answer is easier, but more expensive: Do you/will you listen critically to a fair amount of high quality SACD, DVD-A, and Blu-ray multi-channel music? If so, get the Synchrony One Bs and don't look back. A fair number of multi-channel recordings utilize the rears for instruments and backup vocals and since music tests a system far more than movies, surrounds using the same drivers and having the same "voice" becomes more critical. You will also not compromise movies at all going that route. It's also important to keep in mind that speakers give you the most bang for your buck in a system, although the surrounds get into a grey area here, hence this debate. If the answer is "no" to multi-channel music, then the answer becomes more complicated but possibly cheaper. I would then ask a second question: Are you an action movie junkie? If "yes" then better surrounds might be worth it, as it really does make a difference having a speaker from the same product series when a helicopter circles around the room, although these type of pans are rare. If you're not an action junkie, then going with cheaper surrounds make more sense as very few non-action films utilize the surrounds for more than ambiance, which can be handled by just about any speaker.
But then there is the issue of your 5-channel amp and aesthetics. On the one hand, it seems a shame to "waste" two of your high quality amp's five channels on inferior speakers. Also, having matching rears is nice for aesthetic reasons and it's arguably strange to have such expensive fronts with such cheap rears. The Imagine Bs have a real cherry finish like the Synchronies and probably sound similar, but they're only a little cheaper than the Synchrony Two Bs which are only a little cheaper than the Synchrony Ones Bs. Ah, the going up the ladder seems to never end! On the other hand, it seems silly to spend a lot of money (more than many people's entire system costs!) on rear speakers when something far cheaper would work just as well for the vast majority of movies. Perhaps the mid-priced Image B6s in cherry (vinyl) might be a nice middle ground. It's not an easy choice and one that I've always had difficulty making. I think it comes down to the two questions I asked, how important aesthetics are, and what you can/are willing to spend.
As far as subs go the JL Audios are awesome if you can/want to spend that much. A system like the one you're putting together warrants it, although HSU and SVS are great "bang for the buck" subs. Members in the sub forum should have some good advice for you.