My guess is that you are seeing a variety of numbers because some are "peak", some are "reference", and one of them just seems plain wrong
My recollection was that line level RCAs were pretty much normalized to something like 0.775 volts. This happens to give 1 milliwatt into 600 ohms but these days everything is solid state so nobody cares so much about matching impedences -- it used to matter more with transformer outputs.
The Rec Out number seems funny, I don't understand that one. Bottom line is that pretty much any analog signal on an RCA jack is supposed to be compatible, with the obvious exception of the digital coax out from a player or SPDIF card.