Interesting thread.
I used to use the SIs a lot in the early days. I still have some projects that use them.
If you can open their respective .sfz files, and you know what you're doing, you can add and edit velocity parameters, as well as a host of other triggers, to the files. But they will only work IF the instrument is capable of responding to them.
Editing .sfz files manually can be tedious and take a lot of time if you're up to it. Save the originals in case things go wrong, tho.
Also, you should be able to load the .sfz files into another instrument like Dimension Pro or whatever and see if they respond better.
Another thing about SIs is that they are a little unstable and sometimes unpredictable. I used to have them skip notes and do other weird things on playback.
What I liked about the Bass is it's slide function. It's pretty simple but effective and adjustable.
Steve