Your cable box is probably sending the signal to its "preferred" location, but using the same settings for both optical/coax and HDMI. So you may not have a HDMI-specific setting so you probably get on HDMI whatever is sent to SPDIF.
Or, you either have a DVD which is fertilizer-friendly (crappy) or simply buggy.
For blu-ray, I was refering to the disk's (not the player's) audio track to see if one labelled "Dolby Digital 5.1" would work better than one labbel "DTS HD-MA".
My recommendation to you if to use component for your DVR. Component will give you 100% of the quality you get from cable and will not confuse the optical/coax digital out.
