Should I upgrade home theatre to one with HDMI?

Hello - I was wondering if someone could give me some advice. I have a Denon 5.1 channel amp and pre amp that does not have an HDMI input. I recently got a plasma TV and wanted to hook up the home theatre setup, but was dismayed to find that the input and outputs on the directtv receiver don't correlate with the inputs and outputs on the Denon. Currently the television is connected only to the directtv receiver with the HDMI cable; i.e. only sound coming from the television. Is it time for an upgrade to a receiver with HDMI inputs and pass through or can I still get high def television and quality audio with an optical video feed and a coaxial digital audio feed? Any help or advice would be appreciated. Thanks, KMW