Cable tv image quality
So I have this projector ceiling mounted on a 120" screen. Blu-ray's look fantastic, but I also use it for cable television watching, which I get with Comcast running through a TiVo mini box. I am not nearly as satisfied with TiVo image quality, and not just because it obviously isn't going to look as good as blu-ray, but that it doesn't even come close to what my 60" plasma achieves. For the most part close-ups look good, but wide shots really suffer, with lots of grain and artifacts showing up.
Is this just a function of the image being blown up so much bigger and therefore the weakness of the picture becomes more apparent?
Are there possibly any settings out there someone could point me to that might improve a cable television image?