Given that it's apparent you're serious about audio (nice setup, btw), you should consider better than settling for transcoded DD @ 640 kbps with an A3.
Since you seem somewhat budget conscience, I would suggest you grab an Onkyo Professional PR-SC885P prepro. This is from Onkyo's Professional line and is miles above their consumer-grade Onkyo brand receivers that are a dime a dozen. More information at: http://www.onkyopro.com/model.cfm?m=...eamplifier&p=i
I would certainly keep your CA-5 as your primary prepro. Consider this Onkyo more or less as a HT decoder and video switcher. It handles all the optical formats as well as the new bitstreams over HDMI. This means full bandwidth TrueHD, DTS-HD, and the like. It also fuctions as a nice video scaler since it includes a Reon-HQV chip. You get balanced and unbalanced preouts to fit in regardless of your overall setup.
Now, since this is a prepro only you'll need to amp your 3 additional surround speakers. Honestly, I'm not sure how good the integrated amp was inside the Vantas unit. I'm imagine they weren't fantastic, but you should look into amp options that fit your taste. Some suggestions: find a pair of used, reference quality 2-channel amps; grab 3 mono-block amps or one of the 7-channel amps from Outlaw Audio (http://www.outlawaudio.com/products/index.html);
or look into some of the mid-priced amps at Emotiva Audio (http://www.emotiva.com/amplifiers.html
). My personal suggestion would probably be to grab an Emotiva LPA-1. For the price it's exceptional, and you'll have the option of powering additional speakers if you decide to upgrade to a 7.1 setup someday.