I think you would be better off using the high level inputs (instead of RCA) on the subs if they have them. Run speaker wire off the binding posts of the amp or the speakers themselves which would be more tidy and likely a shorter run to the subs.
Subwoofer and preamp output impedance
I'm looking to add two SVS subs with Y splitters from my pre outs. My Cary SLP-50 preamp has an output impedance of 1200 Ohms and my Bottlehead Kaiju 300b amp has an input impedance of 100k. Both values are nominal, and I found no info about impedance at sub frequencies. My question for the electrical engineers out there: Would the use of Y splitters create a noticeable bass roll off (or any other unwanted side effects) in the subs? The main speakers are Klipsch Forte II's. Thanks in advance. Dave.