The 605 is such a good deal...it really does help future-proof you, in that whichever optical format wins (HD DVD or Blu ray), the receiver can handle the high-def audio formats they use over HDMI. Optical and coax can't do these new formats. There's always new stuff on the horizon - such is the nature of technology. But the 605 is so reasonably priced and so feature-packed, unless you're POSITIVE you will not be interested in Dolby TrueHD, DTS Master Audio, etc, it's probably worth getting over the 505. The one caveat is that if the extra $150 for the receiver would be put toward significantly better speakers that you otherwise could not afford, the 505 might be a better choice. Up to you which is more important now.