How is the Speakon connector wired for REL sub?

Hi all,
I have a REL 328 with a Neutrik Speakon plug.
I'm connecting it to an Adcom A/B 535L 60w amp.
The amp has two R/L speaker terminals — "A" and "B"
Usually, I connect my main speakers to the "A" terminals.
I connect my REL to the "B" terminals.
I've watched the videos and have connected the REL Speakon plug (high-level input) to the REL and at the amplifier the Red wire to R+, the Yellow wire to L+, and the Black wire to L-

A couple questions.

1. HUM. I hear a bit of a hum from the REL when nothing is playing. A ground problem, no? Is there a way to connect it differently that will help with that?

2. TWO SETS OF MAINS + REL. If I wanted to connect two sets of main speakers simultaneously, would I just twist the REL wires in with the main speakers' wires at the terminal, still connecting as described above?

3. DANGER? Is (2) an inadvisable thing to do?

I see there's a lot of expertise here, and hope I've been clear. Thank you.

As I mentioned above your questions are answered here: https://rel.net/how-to-connect-my-rel/ find the session that talks about eliminating the hum.

2) Yes
3) No problem.

Try this to eliminate the hum, this should be in the video's I mentioned above, but maybe not.
Using the Neutrik Speakon plug connection as you stated that you are doing, now run a single RCA interconnect from the sub red line input to a red RCA input on your preamp. This should eliminate the hum.

Disregard my post directly above.
Three solutions to the hum problem:
https://rel.net/how-to-troubleshoot-and-solve-a-humming-issue/

The ground is lifted on both my RELs so no hum...one REL actually has a ground lift switch, and when lifted they both need to be lifted and that does the trick. I prefer the angled Speakon plugs...use em in pro gear also but many don't know the angled version exists...if the REL cables are thick (I use Canare Star Quad with the woven covers...looks great..) the angled plugs let you put the backside of a REL closer to the wall.