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


I just purchased two Quicksilver 60w Monoblock amplifiers and a LineStage Preamp by QS.
To connect this REL 328, normally one uses connect their Speakon cable (Red, Yellow, Black ends that connect to Right+, Left+, and Ground) or a SINGLE "low-level" RCA in. But this preamp doesn’t have a single sub out.

REL’s advice is to buy a second sub and attach one sub to each monoblock. Well, maybe I’ll do that, but in the meantime, I’d like to be able to hook up what I have.

Should I orient the amps so that the speaker terminals are close enough together to attach the strands of the Speakon cables? I have been warned by REL not to hook up high level to monoblocks because it will create a ground problem.

An alternative is that I get a Y cable that will bring two RCA outputs from my Preamp into the single RCA input on the REL?

Or is there another alternative?

Advice appreciated. (But please try not to tell me to just buy a second sub.)
hilde45

Sorry but more than one sub in one room seems overkill.Can also lead to standing waves and cancellation not only not doubling bass ability but cancelling each other out in some frequencies.. All seems a bit of a problem really.

@linndec Don't be sorry if that's the way it seems to you. You're mistaken. At least for my room. And you understand that generalizing about this is pointless, since the room's particular dimensions are critical to the number of subs. 

I've googled it for you, just to get you past reflexive opining.

https://mehlau.net/audio/multisub_geddes/

https://www.svsound.com/blogs/subwoofer-setup-and-tuning/75040195-why-go-dual

https://www.audioholics.com/subwoofer-setup/two-subs

I did use the words "seems" and "can".. I was reflecting on what others had said and my own personal experience. I don't pretend to know about all room dimensions? Sound is a very fickle thing both personally and in practice setting it up..