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
No matter what REL claims I submit that the end user owes it to themselves to try both inputs. All systems are different and you never know what sounds best unless you try both inputs. I still prefer my REL Carbon Limited to the JL Audio F112 v2 for 2-channel. I consider adding the RELs to be one the best Audio decisions I've ever made. 
FWIW  I prefer the line level connection with my subs too.It's easier to blend them in and is more articulate, to my ears anyway.
Hi Al,

Get your point, but remember that the main speakers are seeing their signal from the amp...and not the preamp. So, regardless of how accurate the amp is ( or is not) the most accurate signal that the sub can see in relation to what the main speakers see...is from the amp. Which is what REL’s point is.
@jtcf I fail to see how the blend can be easier ( or more articulate) with the line level ( low) connection, after all, the subs are seeing the exact same signal as the mains in the high level set up. That is NOT necessarily the case with the low level connection. Therefore, it is REL’s impression ( and mine) that the set up is actually going to be easier with the high level...and the SQ will be improved as well.
I think in theory REL is correct; however listening is the final judgement. If I or anyone else prefers the sound of the low-level input over the high-level, what REL claims is mute.
@ricred1  Agree. However, be sure to listen to both set ups. If the low level is preferred in your room and system, so be it. Everyone has a different set of preferences, and their rooms and systems are also dissimilar...therefore your result/favorite may be leaning towards the low-level input.