Again.... re-re-read all of the OP's posts.
1) he has an older STB with DVI.
2) has an AVR connected to the TV via HDMI for video.
3) he is using optical from the STB to AVR. That works just dandy.
4) he is unable to get video when using component from the STB through the AVR to the TV (a signal path)
5) he doesn't have component cables to go directly to the TV to test.
6) he only mentioned that composite works from STB through the AVR to the TV
So....... the suggestions have been:
DVI to HDMI adapter
New STB with HDMI
Try to figure out why the component connection doesn't work. (is it the TV, STB, AVR and/or setup options in one of the aforementioned devices?)
I think everyone is aware that the cable provider can/does broadcast 480i, 720p and 1080i and PQ may vary. But, that's another discussion.
If the broadcast is in 480i, there is nothing OP can do to magically make it 1080p.
Well... yes and no. What option/device is best for upscaling?
Let the AVR upscale to 1080p?
Let the AVR send natively to the TV and let the TV upscale to 1080p?
True that with 480i, you can't make a silk purse from a sow's ear, but with 720p/1080i magic can happen.