columbia wrote:I run HDMI from my Mac to my TV and the picture and sound are quite good.
hdmi cant effect a/v quality (per se). when you have a functioning cord and proper connections it sends computer data from your source (mac) to your display (tv).
there are two main problems
-the physical inside of the cord. not ideal for broadband data transmission
-all the drm type schemes associated with it
the handshakes that cerv96 mentioned are almost certainly his problem. for whatever reason his cable box, hdmi cord, and television do not always shake hands quickly enough. that is almost certainly causing his problem. there are a few technologies at work. one is EDID, which is an attempt for the cable box and tv to tell each other what kinds of audio and video signals they are able to handle. sometimes they give and receive incorrect info. the second is HDCP. as a comcast customer i think that should only affect premium movie channels, but i could be wrong. on other providers like time warner it would effect nearly everything. hdcp is an attempt to keep you from copying a/v streams bit for bit. hdcp enabled programming forces every piece of your chain to prove theres no way to copy the stream before it will play it back. not every hdmi device (such as tvs, receivers, or pc capture devices) has to recognize hdcp, but if programming enforces it you wont get a picture.
an example, my xbox 360 (that i bought used for $75 in 2010) will not do hdcp. just refuses to do it even on multiple different hdmi cords and on different televisions. for normal gaming, that means nothing - games work just fine. but netflix, premium movie channels inside windows media center (you can get cable programming on a 360) and my hd-dvd drive will not play. you get an error message about not having an HDCP compliant link. google it - its a bug in some xboxs but there is no fix. if i cared more id want to fix it but using component video works just fine for me.
for the op, your first problem would be gone if using component cords and spdif for audio to your htib is an option.