I received a new v6 TiVo box and connected it through a Denon AVR 2300 exactly the same way as I had connected my old TiVo box. I cannot acces the on screen menu from my AVR anymore as I was able to do before through the old box. I can acces the menu the same on all the other devices such as Xbox, Blu Ray and Fire TV just not through the V6 box.
I suspect this might be due to the HDCP 2.2 copy protection on the V6 HDMI output, obviously the amp needs to be intercepting the video stream in order to overlay the menu, so as it's an older amp that doesn't support HDCP 2.2 it may be unable to do this and is therefore just passing the video signal straight through.
Might be worth trying some different video output settings on the V6 in case that makes any difference (no idea if it will, but might be worth a try)