What connection are you using from the STB? I used the component to my s-video on the card (Avermedia M780). The recent patch they applied to the STBs broke that.If your's is working, I'd like to get more info.
I'm using component out to my Hauppauge HD-PVR. It is a great device, and works very well in MythTV (and is still working as I'm typing this).