REL high-level connection and McIntosh Autoformers

I'm looking to integrate a sub into my existing Harbeth C7 and McIntosh MA6900 setup to fill the lower end for music. I visited a dealer over the weekend that carries both Rel and JL Audio subs. He suggest that the Rel would integrate easier if I used the Speakon interconnect but was unsure how to hookup given the Mac autoformers. The Speakon has +ve, -ve and neutral leads which connect to amplifier speaker bindings (one on +ve, one on -ve and the neutral on the opposite -ve). Any advice on whether a Speakon can be used as directed?