Amp, fully balanced, with sub via speaker inputs

Roscoeiii, i have used both the RCA and XLR inputs. Best & most linear gain and coordination with main speaker seems to occur with speaker level leads to the subs. Additionally, this seems to avoid the dreaded hum that plagues so many subs. Thank you!

Koestner, Thank you for the suggestion regarding the speaker input to the ground on amp plate. I will request help from Sunfire (Elan) but they only refer me to local vendor and i have not received a response yet. I will use a conductivity tester to see if there is any connection (pun intended). Thank You!

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.

Not sure how the Sunfire speaker connections work, but people have had problems with REL subs and class D amps. I think REL has come up with a cable that solves the problem, but their subs also use what may be a unique connector rather than speaker posts for the high level input.

I'd also recommend contacting Sunfire if you haven't already.

And lastly, any particular reason you chose to run speaker level rather than RCA or XLR to the sub? I know that speaker level is what REL recommends but not sure if other manufacturers regard it as preferable or not.