Well I am using a W4S amp MC-1000/500 with a Velodyne DD15 to the speaker level inputs and it works OK. I called W4S to ask them first and they said that the Velodyne uses a floating ground of about 100 Ohms. I don't know about the REL. Look into getting a Carver Z-1 to solve your problem, or check to see if the neg speaker input on the sub is the same ground as the sub plate itself. If it is then do not use without the Z-1.
Amp, fully balanced, with sub via speaker inputs
I have been running Sunfire 12" subs, most recent model, via speaker level inputs from a class D amp, PS Audio G-250, not the integrated, just the power amp. I like it and was thinking of going to the Wyred 1000 series. I asked Wyred and they stated that using the speaker level inputs from a class D amp may damage the amp and the sub. My question is...Does anyone here run a sub via speaker level inputs with a WYRED 4 Sound amp? any problems? Thank you