I see these are in your tree now - a question: what does tvrgb do?

By which I mean does it just "tell" the TV via hdmi info that the signal is
limited or does it do more eg. scale so it really is limited between 16 & 235?

It's a bit hard to tell by testing as it could just be the way my TV behaves -
it looks scaled judging by how much I have to alter black level but IIRC the
HDMI/CEA specs say that all but 0 and 255 are still legal in limited range to
allow for sub/super that occurs "naturally" in video and sub in a pluge for
proper black level setup.