Thought I'd share a solution rather than post a question as it seems quite a common problem.
yesterday I had my Tivo installed and the engineer synced the controller to my Panasonic TV
All seemed fine and he left me to re-wire my surround sound via my Yamaha RX receiver. Connected TiVo to amp with hdmi 1 and amp to TV hdmi1 then ensured amp displayed hdmi1 and checked TV also input hdmi1
All OK and so turned TV inbuilt speakers down to 0 then turned up volume on amp - BUT every time I changed volume either by knob on amp or amp remote the TV screen blanked out for 2/3 seconds although sound continued.
Very frustrating - tried everything - one solution was to plug TiVo direct to TV and use optical cable TiVo to amp for sound - yes this works but can be problematic down the line!
The solution was to change the TiVo settings:
Help and settings
change to Video Output 1080i
choose the auto detect mode
Thats it - problem solved
PS - if those greyed-out channels annoy you just create a 'favourites' list -