cominginsecond,
What happens is that if you cut all the instruments at the same frequency you're actually creating a hole in the entire mix. Also, the muddy frequency is different for different instruments. Plus, 100Hz is usually not where the mud is. In fact the 100-120Hz range is very important for bass information when you play your tracks on small speakers as these usually can't handle the low stuff. That's why your tracks sound gutted. You're ridding them from an important frequency... However, you should also check that the bass and the kick aren't fighting in this frequency range, and try complementary EQ.
A good way to find the muddy, or overly objectionable frequencies, is:
1 solo the track
2 lower the monitor levels
3 set a very narrow Q on your parametric
4 crank the EQ gain all the way up (this is why you want to lower the monitors, so you don't blow them up and mess up your ears in the process)
5 sweep the frequency
You will find some nasty resonances between 200-400hz range. Once you've nailed where it resonates the worst, then cut at this frequency. That's usually where the mud is.
Hope this, combined with the HP filtering suggestions above by others helps.