REL subs with Rowland Amplifiers


I'm having issues connecting my REL Carbon limited subwoofer to my Jeff Rowland 625 S2 amplifier via the high-level input. I connected my sub according to REL's instructions...yellow lead to positive on one channel, red lead to positive on the other channel, and floating the black wire(ground). I get minimum output when connected according to the instructions. When I use the low level input, the output is sufficient and the sub sounds great. Per my conversation with Jeff Rowland I need to ground the black wire by loosening a screw on the amplifier and connecting the black wire, but if it isn't properly grounded I may damage my amplifier. Is there anyone that owns a REL with Jeff Rowland 625 S2 amplifier or other balanced differential amplifier? If so, how do you connect your REL via the high-level input. Is there an easier way to ground the wire than unscrewing the screw on my amplifier. I just don't want to unscrew the screw and prefer another method of grounding the sub.   
ricred1
@ricred1  Richard, what made you pick the Carbon Limited vs one of the other REL Subs. The new S series seems to be where they are concentrating their line. The Carbon series isn't even on their web page, unless you do a specific search. Seems like they don't want to push that model.
@ricred1  BTW, replacing the stock power cord and better still, the stock connecting cable with a REL Signal cable is a BIG step up in SQ for these subs. I highly recommend the Signal cable that they will supply with the yellow and red cables summed for your mono subs.
daveyf,

"What made you pick the Carbon Limited?" I was originally looking at a single No. 25 or dual S5s. After a long conversation with the dealer about my main speakers, the fact that I had a single JL Audio F112 v2, and I listened to music the majority of the time he recommended the Carbon Limited. If it didn’t work in my system I had the opportunity to return it. I was purchasing right at the time that REL was discontinuing the S3 and S5, so I eliminated the S5. I talked to REL and a few other people that convinced me that dual Carbon Limited subs were a better fit than a single No. 25. I’m extremely satisfied with my choice.

I'm ordering the Signal Cables today:)
 @ricred1   Good move on the Signal cables. Signal make some excellent cables at very fair prices, imo.