I really really like bassy music (ala dubstep) but the problem is, the bass is often too "audible" - ie I want to turn up the sub on my S750s and FEEL the bass, I want to be shaken off my chair, but then you can hear it so much that it drowns out the rest of the music.

What is the solution to this? DSP?

The easiest solution is probably the best: Get any EQ plugin and push the frequency range below 50 or 60 Hz (try what sounds best). These frequencies won't make your sound "thick" or unnatural, nor will they cover the rest of the music. More feeling than sound at all.

Always assuming these frequencies are existing on your record!

If this doesn't work in the way you want, there are (hardware) effect-devices which create an additional bass to your record one octave under the original bass. No idea if something similar exists as a software-plugin for any audio-player...

I think the ATSurround plugin has helped a little bit, too.

Firstly, I relate to your need because im using the same speakers as you are, s750s.
They are excellent speaker, especially for movies and games, yet their weakness is with MP3s.
We all now that MP3s normally sound crappy, especially when not ripped well, but s750s make MP3s sound extremely crappy.

After playing around with different combinations of DSPs, I eventually ended up with a setup that makes MP3s sound more or less as good as normal audio files.

this is what I did, actually im currently at work, so I will try to remember what my setup at home is like:
I loaded the following DSPs in this order:

1. George Yohng's VST wrapper
- Loaded a damn good VST EQ, of which I only mess around with the high frequency and the mid frequency to restore the ones lost in MP3s. At this point, the source is stereo.
- Then I load two more VSTs, cant remember their names, but I use them to add some depth to the sound.
- Then I load the VST that does what you want: BASS EQ. It makes the BASS deeper, clear, smooth, and ground shaking. Without distorting it.
- Lastly I load a good limiter.

2. Channel Mixer
- I set it to output 6 channels.
- Set up mixing to OFF
- Set enable the sub hoover
- Leave the volume at 1.00
- Set bass redirection to leave the satellites intact

3. foo_dsp_vst
- I only load V.I VST plugin to fill up the empty rear chanels since I didnt do an up mix with the chanel mixer.

The sound, sounds great at this point. From treble, voice clarity, to bass.
The only problem is that s750s are 7.1s while the sound is currently 5.1. Meaning that the side speaker are just on display. The one way to fill up the side speakers is to let your sound card drivers do that, but I dont like to let the sound card do any form of upmixing with music, its fine with games and movies, but not with music. So I solve that problem in the next step:

5. Matrix Mixer
I use Matrix Mixer plugin to copy front output to the side channels.

6. All that debatable output plugins: KS, ASIO, Direct Sound
I tried ASIO4All, but I couldnt properly map all the channels to the sound card, so Im using KS which does it quiet well.

7. Im using X-Fi Xtreme Music Sound Blaster 7.1 sound card. In Music creation mode, because in this mode I can resample to 96k and 24bit.

Now I have sound coming out through all 8 speakers, and sounding great.
Listening to music on my pc has never been this pleasant.
But of cause, sound quality is objective per each ones listening preferences.

But to answer your question as to which plugin you can use to enhance the sound of your LEF, when I get back home from work, I will post the name of the VST plugin I use for that.

Could you name the VST's you are using?

Actually I'm looking for something that's able to create equal bass contours for different tracks (I find it annoying that most 80s music lack bass compared to todays releases)

cybasoul, count me in queue too.
Can you post details about your setup?