If it is less than 10 feet don't bother buying a new cable. Connect a RCA cable itself between STB to HTR. (Not recommended solution, but you will not see much difference. There is huge debate on this topic)
I checked the SPEC of Philips HTD 5580/94 and don't see a Digital co-axial input in your receiver. So, it may not work for you. I don't think any D2h STB comes with Optical audio out.