When testing the response of a subwoofer you want to disconnect all other speakers and test the sub by itself with the receivers crossover set to the frequency you normally use (i.e. 80Hz).
I don't see any 2001 series subwoofers on KEF's rather horrible site, but I do see that they have a 2005.2 series with a frequency bottom of 30Hz. I am assuming your sub is in this range?
Either way, it isn't extending very low and I guess you're not getting much low bass in the sound. You're really listening to what's called one-note bass that is around 65Hz. Not too good.
You need to test the sub alone and try and place it in a corner of the room that produces the best low end extension. REW makes the testing fairly easy. You can move the sub around or alternately place the sub in your listening position and move the microphone around to the corners to find the best spot.
brucek