Sub woofer power cable?

The best interconnect for a subwoofer is the Audioquest Wild
Dog. By far the best subwoofer interconnect I ever tested. It
is 100% silver and very thick. It is fast as a rocket and the
best dynamics you will find on the market.

http://forum.audiogon.com/cgi-bin/fr.pl?rcabl&1400104392

read the review

You have already upgraded the line-level signal cables for your RELs?

I have tested many powercables on subwoofers. I had the best results with Purist Audio Design powercables.

I stuck a large power cable on my REL sub along with PS Audio Power Port plugs for it and the main system (the sub needs its own plug since it's not near the other gear). Not sure the sound of anything got better, but it made me feel better about the AC. Bass "tightness" usually really means less overhang or lingering room sound.

IMHO, power cables aren't going to give you what you are looking for. I'd try room placement....and it's free.