Hey everyone. Great place you have here.

I searched but didn't find anything relevant, so here's my situation:
I just got a new plasma TV and upgraded my cable box to the SA 8300HD PVR. I wanted to connect that cable box to my Philips "HTIAB" 5-disc behemoth, which is about 6 years old, using the digital coaxial audio output/inputs on both units. The Philips does not have optical, just coaxial. The SA8300 has both.
When I connected the two with a fresh new 75ohm digital coaxial cable, the volume from the speakers was barely audible even when cranked to 100% on the Philips unit. Obviously being digital the SA8300 volume controls didn't do anything.
The volume is way too low to be at all useful, so I have temporarily gone back to the traditional red/white RCA connections. I'd like to use the digital connection, as the Philips has surround sound and a sub. but maybe the true surround only comes from that unit when using a DVD through the 5-isc changer? If so, that sucks, because I'd love to have surround sound with digital cable as that's what we watch the majority of the time.
What can I fiddle with to get this to work? Or is is simply a limitation on the Philips home theater that it cannot accept the digital input from the cable box? (But why have the jack if it can't be used?). There are settings in the SA8300HD that I have tried, such as Volume: Variable of Fixed. Audio: Dolby Digital, Other, or something else. Or Audio: Auto DVI/HDMI, Digital Out, or Other (for use with RCA's).
Thanks for any help you can provide!
Cheers.
Eric