I had the same problem and tried all sorts of power insertion devices for HDMI. I finally ended up using a powered HDMI switch and was able to get rid of the sparkle effect of my long HDMI run. I bought the powered HDMI switch from monoprice. They have plenty of options.
You can also try "simplifying" the HDMI signal. Set your tivo for 480i, then 480p, then 720p, then 1080i. Try each setting and see if you can get the signal to work. In my experience, the simpler the signal, the longer it runs.