REL subwoofer crossover question

It is my understanding that the neutrik connection works with most amplifiers and because the output signal matches exactly with the amplifier, not the preamplifier output signal, a more exact output match is created. What I have found, I think you did as well, is that the output signal is stronger when taken directly from the preamplifier so you require less volume to get more bass output. Over time, however, it has been my experience that when properly mated to the amplifier via the neutrik connector the bass response is more realistic and creates the illusion that there is no subwoofer at all because of the better integration. Long term the REL subwoofers with the neutrik connection in my systems, I am a subwoofer addict and have had many different brands/connections in various systems, have been the best subwoofer integration experiences.

Not sure why the neutrik connection does not work with differential balanced amplifiers. I beleive that it has to do with negative feedback and that differential balanced amplifiers either do not offer it or offer too much. Someone technical would be able to offer a better explanation. Either way in one of my systems when using a neutrik connector the Storm III, great subwoofer, would emit a loud pop that would scare the hell out of me. I cannot remember which amp it was, but I was advised by someone at that time to use the preamp output connection.

This may sound simplistic (and might actually be wrong) but somebody at a "boutique" hifi place told me that when hooking up the REL to a Class D amp you connect the 3rd wire to ground on the amp chassis (the other 2 to left and right positive speaker plugs).

It is a ground issue with some 'D' series amps. REL addresses this in the operators manual of their newer models.

The Neutrik connectors from the amp assume a common ground plane, that's why there are only 3 wires (R+, L+, either -) and not 4. A balanced amp does not have a common ground plane. So you can only get one channel into the sub with the Neutrik, at best. You need to connect the sub to the preamp via RCA's if you have a balanced amp, or get 2 subs.

I think in the case of a balanced amp, you would need to connect the ground wire to a ground lug or screw on the the preamp, which should give you a common ground for each channel. This is not entirely clear in the manual for my B2, but it has worked fine for me (I have a BAT balanced amp and preamp). The manual shows this connection configuration for mono amps, and also mentions (albeit not very clearly) this configuration for a differentially balanced stereo amp also.