Problems with my Chiro c 800 and 5.1 decoder

Howdy, I picked up a Chiro c 800 and a 5.1 decoder pretty cheap on Craigslist. I'm running it to a 5 channel ATI amp through PSB Imagine B bookshelves in the front and some cheaper Energy speakers in the rear. I have the decoder hooked up to the preamp as well. The problem I'm having is I'm not getting any sound in the prologic mode, only in stereo and enhanced stereo. It's faint and I can only hear some sound when it's turned up all the way My question is if there is definitely something wrong with the unit or if possible there is a connection problem. Perhaps the cable I got for the decoder is the wrong one. Anyhow, I really like how the Chiro sounds in stereo mode and since I listen to a lot of music on it, this is important. Would it be worth it to fix the unit or put my money towards something modern? If anyone has a copy of the manual that would be a huge help too! Thanks for your help.
Many units won't take a digital or 5.1 signal and down-mix that for pro-logic. You will have to have a stereo/2 channel signal for it to produce pro-logic sound. If you are only using 5.1 or digital out from your dvd player, that's the problem. You may need stereo outputs as well.

Should be a pretty nice sounding system once you figure it out.
Yeah im using the rca out of my blue ray player. As soon as I switch it to pro logic it cuts out but you can hear some faint noise if you turn it up all the way. No one here in Austin works on Chiros so I'm wondering where I can take it to. I'm contemplating about getting a different unit but I'm really pleased by the 2 channel sound for music, which I spend a lot of time listening. Thanks for your help, Ragnar