OP, sorry for going off topic.
@ross6860 Thanks for the clarification - there is no mention of this in the manual but it makes sense (it’s the same). Connecting to the speakers could be more convenient and maybe help reducing hum (if any) by reducing the length of the supplied cables - which are 60Hz antennas. It would not work for me as I’m using my mains for both stereo and a/v (by manually switching speaker cables).
@tony1954 I think we are both saying the same thing, or close. refer to page 15 in the manual. The black wire in the speakon cable is a ground and referred to as negative and ground in the manual. Differential and Class D amps use the same method.
My REL dealer said I should "float the ground" if there was a hum in my system, which there was (Initially the amp was a Line Magnetic, no pre or sub-outs, not differential). Floating the ground/black wire helped but trimming the 30ft cables also helped a lot but didn’t cure the issue 100% in one of the RELs. Re-configuring the red and yellow connections in the speakon connector itself eliminated the hum completely (I called REL and talked to Frank at Signal Cable who makes the speakon subwoofer cables and both agreed it was safe to try prior to doing this).
For stereo set up, the manual is actually pretty poorly written. p18 1.a refers you back to pages 11 & 12 where there is nothing mentioned about stereo set up.
In fact stereo set up is really the same as the mono-block instructions on page 16 except L & R terminals are on the same amp, and again, in my case floating the ground/black wire worked best.
I did experience the high gain issue mentioned on p16 btw.
When I bought the Raven amp, I discussed wiring the subs with Raven and James strongly recommended using the RCA connections. I again called REL to get their opinion and they said use whatever method sounds best.
