but a DIGITAL coaxial cable. There's a difference.
Here's the 'recipe' you should try for connecting everything. Comcast outputs should be active simultaneously, so that particular 'split' should work fine AFAIK. Getting the LG BD player to send audio correctly may require you to forego HDMI and use Component (RGB) instead to the HDTV. See below for options.
Comcast DVR (HDMI out) --> (HDMI in) HDTV
"" "" (digital optical out) --> (digital optical in) Pioneer AV receiver
LG BD player (RGB Component out) --> (RGB Component in) HDTV
"" "" (digital coaxial out) --> (digital coaxial in) Pioneer AV receiver
*If you would like to also try sending audio 'out' from the various SmarTV apps, use/connect another digital optical cable. Plug it into the digital optical output behind the HDTV and connect it to the digital optical input behind the Pioneer.
Use the HDTV remote to control video inputs & smarTV apps; Use the Pio remote to control audio.
7.1 & advanced audio tracks from Blu Ray player won't be available since the receiver doesn't have HDMI, and the LG player doesn't have multi-channel analog output.
Post back any issues you still have.