in Logic..? then resample only little bit of the modulation and trigger from different locations? Perhaps they set up a filt env first for the attack of the bass then a delayed LFO kiks in modulating the cuttoff of a low pass.?
Yeah man there's lots of things to do to twist em up. Usually, doing the mod wheel by hand is the most effective.
First off ... in order to have real control over the sound I might recomend starting with a synth and getting to know that reals well. Then, when you have made the baddest sound you can muster on the synth, resample that biatch (preferably through a tube or other analouge comp) into the emu. Once it's in the EMU treat each sound like a separate oscilator (Remember not to do this with the sub/bottom layer if you are runnning it out of a stereo channel - I dunno why you'd run it stereo in the first place but anyweah) meaning make 2 (usually that's enough) voices and detune them by about 4 - 10 cents each (one at -4 the other at +4, ya dig?). Then group them. Copy these groups exactly so that you have the same sound in each octave (or 2 if ya want). Now take the first group and put it on a low pass (of course you could use any filter) that's set to 120 Hz (and you could use any value really) then have an LFO+ mod the filtfreq by +100%. Now take the second group and set the low pass to 20KHz. Take the LFO+ and set it to mod filtfreq by -100% Now take the third group and set it to 1KHz and have LFO~ mod the filtfreq by +100%. This should give you different stages in the cycle.
Also, like I said before, you might want to try moding each filtfreq with 2 LFOs each so that the pattern is not as predictable.
In addition, don't forget to use all the tools available to you. Add a bit of pornomento (OK I know that's not it) or use the Aux Env to control the pitch (ie. have the note quickly rise into its pitch ... or quickly fall) also get a good Amp/Vel (they call it different things on different screens) Env going to shape the tone. Get different groups of the same sound on different filters/cutoffs/resonaces, some controled by hand, some with LFOs, some with ASDR envelopes. Layer your basses over subs. Use multiple layers (this requires a bit more skill to do more that a sub and upper bass). Use the gain function to digitally clip your sounds for a tearing high end. what else ... there are unlimited options ... don't forget to use your synth to start as you can effect pulse width and sync (including things like sync skew and formant width) which give you much more control over the sound.
Anyweah, I'm rambling ... hope this helps