Not uncommon. You need a decoder/processor, which will take a digital output (either optical or 75 Ohm coaxial)and covert it into the six channel 5.1 Dolby Digital/DTS(Main R & L, Center, Surround R & L, Subwoofer or LFE). Try the Technics SH-AC500D or Yamaha DDP-2, you can find them reasonably priced on EBay.
Get a new receiver. You can get a receiver with DD and DTS decorders for $100-200 new if you look around, probably cheaper on Ebay. From my experience, the 6 analog inputs aren't as good as using coax or optical, even if the signal is straight from the DVD player.
I just bought a Philips PH61155. I was excited when I got home, I want to listen to Sirius without the TV on. I'm going to again today, I have hooked it up by the instructions and split the coax and ran deadhead into the unit. I think one of us is on drugs and it ain't me. No lights are even coming on. I will post when I beat this.
A coaxial cable used to be the standard way of connecting VCRs and cable hook-ups to your television set. It is a single cable with a metal pin in the middle of it. However, there are now more options of cables, such as RCA cables. If you have an older television that only has a coaxial cable output and a DVD player that only has RCA outputs, you need a way to convert the coaxial cable to RCA.