Many speaker companies make (or will make on request) a subwoofer speaker cable with Neutrick connector for RELs. Just look around. And usually less costly than baseline blue.
I have two. One from Audio Art and one from Signal. The Audio Art is about twice as much (but still less than price of baseline blue) but is better constructed, better connector.
On the list of cable importance, sub power cable and sub speaker cable are much lower than power cables and speaker cables to amps and sources. IMO. YMMV.