If it has a set of 5.1 analog inputs you can keep it. Some old receivers were sold as digital ready and had these inputs, my old Onkyo did. You would only need a Dvd player with built-in decoding.
There was a company (or product?) called Vantas they made a unit that was an add-on at about the time the movie industry was switching from pro-logic to dolby digital. There were two models (Vantas DPA-P87)(Vantas DPA-S50), these show up used at Audiogon and E-bay, A Vantas DPA-S50 just sold here on Audiogon the other day.
I don't remember which model you would need, but one of these two will do what you want to do and can be used with even a two channel receiver. It was a short lived product because all it did was fill a gap at the change over between DPL-DD. A google search of each model # will find some reviews for each and should help you figure out which model you would need.
As far as I know, this was the only product of it's type ever made because it hooked into the system at speaker level which did away with the need for 5.1 inputs for add-on.
Thanks for the info. As far as the first item goes, I checked my DVD player (Mitsu DD-8020), and it does have the on board decoder (holy crap, something current in my system??!!). Alas, however, I checked the back panel of my CT-28V to find only stereo inputs. So, I'm guessing that outside of direct wiring the DVD straight up to the backside of the amp, and running the subwoofer (.1 channel) out of the DVD and straight into the sub, I'm SOL with the simple road (assuming nothing fried when attempting this, seems kind of brute force anyway).
I will look into the Vantas stuff, but I am curious to hear your thoughts regarding the Marantz unit (which I believe is listed in the Audiogon classifieds) or the Adcom unit.
Thanks again for your quick response, I do very much appreciate it.
Unless the Mitsu has volume control built in..Do Not Try hooking it to your amp. The older Sunfire Theatergrand II is a Bob Carver design and brings with it some of the Carver sound and features which you may like. (I own this older model myself).
You can find these used for around $1,200. This unit does not have all the latest bells and whistles, but does have all you may want or need. I mention this unit only in the context of you wanting to stay with what you seem to like and my guess is that the Sunfire would give you what you want and even better sound quality. Carver likes to voice his SS gear towards what he considers (tubed like) in sound. While I've never listened to your pre-amp nor do I know it's features..my guess is that the Sunfire may share some of them.
On the other hand, you could pick up any number of used pre-pro's with DD/Dts decoding for around $400-$500 here on Audiogon and this would also allow you to keep your amp. As a matter of fact, you could even keep your Carver pre-amp in the system as a two-channel pre and simply let your Pre-pro's signal pass through it when watching movies.
As far as the units you asked me to comment on, I don't have any experence with them so hate to comment. You could post a thread on them, others may have used them in their HT systems. Hope this helps a little.
P.S., Check the back of your pre-amp and see if it has a DB-25 computer type input on it. A very few products have had these as 5.1 inputs. Onkyo had this on some of their older stuff and Sunfire (Carver) have also used these at times. My Theatergrand II uses one also.