Listening to the sample, seems like the problem is mic placement. It's not that the low end is overpowering--it's that the top end is muffled. You can improve that in post-processing by adjusting EQ--even in a program as basic as a freebie like Audacity.
But it would be better to get the mics up higher--even if you clip them to the arms of your glasses or something.
You have them on your shoulders...are there people in front of you?
On the SoundPro site, the CMC-8 are cardioids--the BMC's are binaural (omni) and the CMC are cardioids, unless you bought the optional omni elements.
http://www.soundprofessionals.com/cgi-bin/gold/category.cgi?item=AT-P12100Are you careful to stay pretty still so that the mics are always pointed directly at your sound source?
With directional mics, what is picked up off-axis (not within the directional pickup area) can also sound muffled.
I don't know how stringent the club is, but in most places, when the lights go down, no one is going to notice visible cords. People walk around all day now with earbuds hanging out, or have earplugs on cords. You could clip them to your glasses and loop the cord over your ear and probably not get busted. Try that at home first, though, to make sure you wouldn't be adding noise from the cord to the recording. Otherwise you might have to let the cords dangle--which still probably wouldn't get noticed.
If you're really worried about stealth, you could also try the Sound Pro TFB-2, which go in your ears so they look like earbuds or earplugs. But the capsules in them aren't as good as the ones in your CMC-8.