Low freq rumble, and using a KAB Subsonic filter.

I posted this in the Cable section here on A'gon, but thought it might be a good idea to post here in the Analog section also, as it directly pertains to an issue I'm having with my Analog set up.
After adding a REL sub, when using my tt, I'm getting a low freq rumble from my sub. A friend is going to let me try his KAB RF-1 subsonic filter to see how this works out. I have a couple of questions:
1. Should I insert it between my phono preamp and preamp, or
Should I insert it in my tape loop? Sonically which would be best?
2. Will my choice of interconnects be an important consideration as to use with the KAB? Is there a good, inexpensive interconnect that you recommend for use with the KAB?

In advance, thanks for your input regarding the use of the KAB
The KAB RF1 website states that you can put it in either place. I'd recommend the tape loop so that you can easily try it both in and out of the signal path. IMO if it eliminates the rumble problem but effects other areas of the music than you will want to get an infrasonic filter that filters out anything below 20hz and does not mono everything below 140hz. IME there is stereo info at least another octave lower.
It is designed to go between the tape loop or between preamp and amp. I use mine through the tape loop and switch it into the circuit when I listen to vinyl. It has removed completely, all rumble from my system and stopped the woofer cones from oscillating. I am using 2 pairs of MIT AVT3 interconnects, at less than a hundred per pair.
Does the noise vary with volume or is it just fixed no matter what the volume?