This information doesn't seem to be publicly available. (On that note, the website that the TruTech Filter Wheel page on this website links to,
www.trutek-uk.com/cwss/USB/ssu2.htm
, is a 404.)
I have sent them an email.
In the meantime, I could test whether the driver responds to an increased number of filter slots, if you could show how to add the property?