Hey logicluvva,
This is what I'd do... say we have 10 audio files for each intended velocity layer and 3 intended velocity layers...
1. Record the audio into Logic on 3 audio tracks.
2. Clean 'em up as desired and then split at transient points or cut them up.
3. Select all the audio regions on that track, right-click and choose: Convert > Convert to new audio file(s)
4. Name those files as appropriate - although naming the regions before hand might be better.
5. Repeat step 4 for the other audio files per track.
6. Open the EXS24 Inst Editor and choose Zone > Load Multiple Samples. Then select all the harmonics (for ex.) and import them from the start of whichever note they should be at, e.g. C1.
7. Repeat this for each set of audio files (per velocity layer) and they'll be stacked on top of each other and within their own group!
8. Once done switch to Group view and choose View > Group: Velocity Range
9. Now set the velocity range for each group. i.e. double click the Lo value and set 0 and the Hi value and set 55. The next group would then be set as Lo=56 and Hi=80, etc... of course choose the velocity value to suit you :)
Looks like lots of steps... but it's quicker to do than explain :) Perhaps that's a bit of an old school method - but I find it kind easy... instead of numerically adjusting the velocity layer for the group you could visually drag the velocity layer edges in the "Show Velocity" mode.
Hope that helps!
Rounik