You should download the wireless app for your speakers and see what controls they give you on the sub output. If you have a choice, I'd start with the crossover at 80hz with a 24db/octave slope.
Some subs have parametric EQ (SVS Ultra does) so that you can compensate for room nodes.
The sub will have FAR lower distortion at bass frequencies than your Kefs. At 50hz the distortion of the regular LS50 is only 20db below signal level. Even at 100hz, those little midbass drivers have major distortion.
http://www.soundstagenetwork.com/index.php?option=com_content&view=article&id=941:nrc-measur...
Some subs have parametric EQ (SVS Ultra does) so that you can compensate for room nodes.
The sub will have FAR lower distortion at bass frequencies than your Kefs. At 50hz the distortion of the regular LS50 is only 20db below signal level. Even at 100hz, those little midbass drivers have major distortion.
http://www.soundstagenetwork.com/index.php?option=com_content&view=article&id=941:nrc-measur...