You will see where I am at technologically w/ this question. So if I got a receiver and ran it through the Carver would you then get the power of both the receiver and the Carver?
Nope, can't do that. If you get a receiver and use it in conjunction with the Carver amp, you'll essentially be using your new receiver as a pre/pro, ignoring its built-in amplifiers -- unless you want to use them to power something else.
Your considerations for getting a new pre/pro may will most likely be features. If you are only DD 5.1 right now, you're missing out on DTS and any 7.1 stuff (if you're interested; I personally have the equipment to do 7.1, but just stick at 5.1). I bought a pre/pro (the Outlaw 990 mentioned) just to get newer processing and especially DTS. I was previously using an old Denon receiver.
Would there be any reason to get a receiver vs. the prepro?
Currently, receivers seem to have more features. These big companies (Onkyo, Denon, Yamaha) simply have more resources (engineers, money to flush if HDMI didn't pan out for some weird reason, etc.) than do the smaller companies that would manufacture a quality pre/pro. So, while there are a few receivers out that support TrueHD audio processing via HDMI, there aren't a lot of receivers.
Of course, if you wish, you can have your HD-DVD player or BluRay player do the decoding and go with 5.1 or 7.1 into your preamp, rather than relying on the preamp to do the decoding via HDMI. I personally just "upgraded" my Outlaw to a preamp that has zero video switching and zero HDMI inputs. I got tired of the confusion, the HD/BD format war and everything else. I'll either go in analog, buy the companion video switcher/HDMI processor or buy a new preamp when the time comes.
I have to put the volume up pretty high to drive the speakers- but I don't feel the need to go louder w/ my current set up.
Turning the volume up is OK as long as you aren't clipping your amp and/or distorting your speakers, and it doesn't sound like you're complaining about that. If you're happy with your power and volume available, I'd probably stick with the amp you have.
Since you've already gone the separates route, I'd probably just stick that way; there's no good reason to go back to a receiver, unless you just want to get rid of one box. If you're at all interested in the Outlaw, I'm selling one
here -- PM me and we'll work a deal!