Actually, an RCA cable (single) won't deliver the DD or DTS encoded traffic. a TOSLINK optical or coax digital will, though.
To help "future-proof" (as much as could be done anyway) your equipment, I wouldn't choose anything that won't accept audio from HDMI. All the new lossless surround formats (Dolby TrueHD, DTS-HD, etc.) (and multi-channel SACD) will only work via HDMI if you want your pre-amp (or receiver) to decode them. Otherwise, you'll need the player to decode it and send it out over 8 channel analog to the pre-amp. TOSLINK or coax digital cannot carry enough bandwidth to transport all this data. Ain't progress great?
Back to your amplifier question - I'm running my front 5speakers (KLF-20 mains, KLF-C7 center, and KSP-S6 surrounds) from a 5-channel amp (Emotiva XPA-5, which is 200wpc x5), and currently running the rear 2 surrounds (which are non-matching Klipsch KV-2 centers) off my old receiver while I wait for the Emotiva UPA-2 to be released.(125wpc x2).
I wanted to make sure that the main 5 channels had matching timbre and amplification for 5.1 SACD tracks, and for HT, it seems to me that far more information comes from the side surrounds than the rear surrounds for 7.1, so a little mis-match won't hurt on those last 2 channels.
The Emotiva amps are an incredible value, and are often reviewed head-to-head against products costing 2-5x as much. The XPA-5 is $799, and the UPA-2 will be $299. There's also the UPA-7 that does 125wpc x7 for $699. Keep in mind their power ratings are always conservative, and done with all channels driven to maximum output. For example, if the rear channels aren't demanding much but the fronts are, the amp can supply more power to the fronts.