A BIG thanks for taking the time to answer & advise Ben
The new Samsung IS 4K - I presumed it was 'backwards' compatible and would be fine with a lower level input? It's the TV that is being 'added in to the loop so, as far as I understand it, is simply taking the feed that is already being outputted rather than dictating it?
The older Sony (that WAS the sole output of the Tivo before) is 1080 capable and was working fine with the Tivo before.
I've not changed any settings on the Tivo and simply repeated what I'd done on the secondary box with this powered splitter?
I've checked and its still set to 1080 (& lower) as it recognizes that the TV (Sony?) isn't capable at owt higher.
If I unplug the splitter and plug the Tivo direct into the Sony, Amazon Prime et all work fine, but stop if I put it thru the splitter - which it DOESN'T do when using the same splitter and cables from the secondary box?!?