How to connect monoblocks to a single REL sub with ONE RCA input

@almarg 
Connections, Subwoofer speakon connectors to monoblocks:

Red to Right +
Black to Right -
Yellow to Left +

Regarding outputs that are "balanced or bridged" I don't know how to tell — but if it's indicative, there are only RCA connectors on the preamp's outs and they run to RCA inputs on the amps. 

Interesting point about the un-connected approach to the black ground wire. If I heard a hum, I suppose I could try disconnecting that wire.

I appreciate your taking a look at the mono/stereo device mentioned by imhififan. In some ways, it still seems like the safest way to go, but I can testify that I tried both high level and low level inputs tonight, and high level is far superior and it's drawing on exactly the signal being sent to the speakers.

I continue to admire the clarity and concision of your replies, and the time you take to research someone else's (my!) question. Thank you.

@hilde45  Is that set up the one suggested by REL? I used that exact set up on my prior ARC stereo tube amp, and it worked fine. I also use that basic set up on my ss balanced stereo amp...although I place the Black to a grounding connection on the amp...as I don't think the minus is a true ground. Works well too, but this is with just one sub connected, not two.

That all sounds good, David (hilde45). And looking at the manual for the amp in addition to its description at the QS website I'm certain that none of the exceptions I cited that would necessitate not connecting the black wire to a negative output terminal apply in this case.

And thanks for the nice words. Enjoy the new purchases!

Best regards,
-- Al
 

Regarding your recent question about the device suggested by @imhififan , when I looked at the links he provided what particularly gave me a fair amount of confidence was the statement on the packaging that can be seen in one of the photos, that "it provides mono output while retaining L/R input isolation." I interpreted that to mean that the left input and the right input are isolated from each other.

Thanks @almarg for clarify, the MCM converter is utilizes an independent 1:1 ratio audio transformer for EACH channel, so the left and right inputs are isolated from each other.

@almarg Great to hear. I certainly want to avoid any issues. I *assume* that if I start to hear a hum that I’ll just disconnect the setup. I asked QS in several emails about grounding to preamp chassis and that suggestion wasn’t even taken up in the (very sparse) replies.

@daveyf

Is that set up the one suggested by REL?

Not for monoblocks. If you look back at some of the REL links people shared above, you’ll see that REL suggests NOT connecting the sub's high level connector to monoblocks. They recommend using the "low-level" input. My problem (as described above) is that my preamp output is stereo and the REL I own only has a single RCA input.

 My sense is that the advice they’re giving here is somewhat inexpert and/or poorly researched. I am not confident that my question got to someone with sufficient knowledge and/or they didn’t really stop and think hard about the question. Their suggestion of a Y cable would (as QS, almarg, told me) collapse the stereo field for the main speakers. While I sympathize with REL’s predicament of having many customers with a wide variety of products, it would be better to say "we’re working on your question" than to give erroneous advice.

I used that exact set up on my prior ARC stereo tube amp, and it worked fine. I also use that basic set up on my ss balanced stereo amp.

I’m assuming by "same set up" you’re saying that you used the high level REL connector. The issues raised by my situation are critically different, insofar as they pertain to grounding the subwoofer’s connection on two separate monoblocks.