REL subwoofer using only red cable not yellow per REL technical dept

@wolf_garcia - yes, I got that from their website:

Here they’re talking about "Balanced/Differential/Class D" connection.

When doing so, please combine red and yellow leads together to form a single composite “+” or “hot” conductor as shown in the diagram below. Do not connect the black wire to the output terminals. Instead connect it to a chassis bolt as shown below.

However, they go on to say:

We do not recommend use of a single REL with ANY brand of monoblock amplifier as it is possible to observe slight channel-to-channel dc offset that can result in mild oscillation. For any monoblock, we recommend use of stereo pairs of the appropriate model of REL sub.

I’ve read issues with some Macintosh monoblocks, and I’m asking specifically about Pass Labs monoblocks with regards to connecting a single Rel sub to one of the monoblocks (using high level connection into sub).

What is a “faster” subwoofer?

REL does indeed recommend two(2) subs if you are using mono block amps. I have mono blocks, so two subs it is. However, the issue becomes that depending on room size, two subs can easily overload your room. In my case, my room is very small, albeit with a vault ceiling ( which adds to volume), so the little T5i is the maximum that I can get away with in this room. I think one has to consider the room/sub interface as a major factor when using two REL's. If you utilize mono blocks and your room is like mine (11x10) or smaller...and without the vault ceiling, I would suspect that you will run into trouble with the various room nodes you are going to excite.

And that's why I only want to run a single sub, it should be plenty. I really don't even need a sub for 2 channel, but I know it will enhance the experience somewhat. I do however require a sub for home theatre. I just wish someone with Pass Labs monoblocks would disconnect one sub from their system to see if there's any low level hum. Is Rel Acoustics saying you need 2 subs as a CYA, or is it 100% guaranteed the hum will exist when running monoblocks with a single sub?

"....REL suggested first unplug yellow wire from speaker terminal and turn up sub gain as that might improve the bass integration...."

Do NOT leave the yellow wire floating! I recently traced a low-level rumbling sound to an open connection between the yellow wire and the Left Speaker input inside the Speakon connector.