I need a longer sub cable to move my sub where I want it. Looking for advice on a rca to rca adapter. Do I risk losing signal? Should I just buy a longer cable? I currently have a 15' but I want to move my sub to a different place and I want to run the cable under my floor so I need about 35-40 ft cable. Any suggestions appreciated.

Panasonic TC-P50G15, DMP-BD60
Yamaha RX-V1400
Axiom M60's,VP150,QS8's
Hsu VTF2