I don't think you will be able to use either 976 output to feed your Tivo or Bluray unless the BDP has an HDMI input. As for how the 976 will respond to longer HDMI cables it is any ones guess, but the HDMI spec is probably pretty specific about the voltage able to be applied at the output of any device. I bought a 30 foot Redmere cable from Monoprice and it works perfectly over that distance. It is only a 10.2 GBPS cable but works well for 1080P. Once the new 4K and HDR devices are common the cables will have to support a much higher data throughput so they will become...
a) more expensive
b) less reliable
c) more subject to snake oil possibilities.