You could use the coax to run component or the CAT5 to run a single HDMI-CAT5 adapter signal. You can't use a dual CAT5 adapter since the audio is sent with the video, not on the second CAT5. I believe the second CAT 5 is usually used for the HDCP signal, and you need that.
If you can, try both the component and HDMI signal (with a temporary HDMI cable) to see if there is any significant visual difference (I assume the receiver also has a component output). If the HDMI looks better, than try a single cable HDMI-CAT5 adapter.
Edit: One negative to using component is that it won't send 1080p, if you want that option.