I own a REL Studio II along with a pair of brand new Allnic M3000 Mono Block Amplifiers and was able to successfully hook them up to each other without any problems. The way I did it is as follows (and just to be clear, when I say right or left, I mean as you stand facing the speakers. So, "left speaker" means, as you face both speakers, it's the one to your left, etc.):
My speakers (Sonus Faber Electa Amator IIs) are approximately 9.5 feet from each other, with a fireplace in between them (any greater distance between your speakers and you will not be able to connect a single REL Studio II to your Mono Block amplifiers without a Speakon, High Gain Cable that's longer than 18 feet). That's because I do not believe in positioning a sub-woofer between speakers. It should always be behind either the left or right speaker; preferably the right one because in most orchestras, that's where the bass section is located.
Anyway, I placed each mono block on the fireplace hearth, just under 1.5 meters from each speaker's terminal connections. I then set the REL Studio II's right leading edge one foot behind the right speaker's cabinet and the center of the sub-woofer, 8.5 inches from the wall. To connect the sub to my mono blocks, I used an 18 foot Speakon High Level Input Balanced, (insert, twist and lock) Cable, most of which I was able to hide beneath a carpet.
At the other end of the 18 foot Speakon Cable, three, 36 inch wires with spade connectors emerge. They are red, yellow, and black.
You run the Speakon cable exactly between your two stereo speakers and then you take the red (positive) and black (negative) wires and connect them to the right Mono Block's positive and negative speaker terminals. Then you take the yellow wire and connect it to the left Mono Block's positive speaker terminal.
In this manner, you're integrating the REL Sub-woofer into the system's stereo signal. I have two (one left channel, one right channel) 7 meter Purist Audio Design Praesto Revision RCA Cables that run from my Allnic L3000 (formerly L4000) Pre-amplifier's right and left outputs to the left and right Allnic M3000 Mono Block Amplifiers' inputs.
Having the REL Studio II located behind and to the left of the right speaker gives me the very best integrated sub-woofer signal possible. I simply use the REL Studio II's Fine, Coarse, and Gain Controls to properly "dial in" the stereo signal coming from my mono block powered speakers.
Hope this helps. Let me know how you eventually hooked everything up.
Smw1950