Connecting a single REL sub to a 440

[fraha]

As it’s a REL, High Level is the way FWD.

But do I simply connect from the positives of both Devialets?

I would ask REL support as I did before i connected my REL to my single Expert 220 pro.
They gave detailed answer:
Hello Josef,

Thank you for contacting us, and for choosing a REL Acoustics subwoofer for your home audio system. While Devialet describes the 220 Expert Pro as being a "hybrid amplifier that offers the best of Class A and Class D technology", we recommend treating it as a Class D amplifier in terms of how to best connect the High Level cable for your new S/510 subwoofer. As such, the following instructions can be used when connecting High Level to this amplifier:
• Connect the red wire of the High Level cable to the right channel positive output terminal on the amplifier.
• Connect the yellow wire to the left channel positive output terminal.
• Connect the black wire to the ground thumb screw, located next to the "Line 2/Phono" inputs on the amplifier's back panel.

I hope that this helps, but feel free to let me know if you have any additional questions or concerns.
Regards,
Jacob Van Sickle
Customer Success Manager - REL Acoustics

It's a good thing I looked into the forum   i was just about to write to REL and Devialet about the connection. I will get a Classic99 by mid september, and the connection thing is cleared in this case for me. Thanks.