Your best option is most likely to be to write the driver yourself.
http://www.hobbytronics.co.uk/usb-host-serial
I don't think you get source code for that. You just get a premade hex file to load into the PIC on their boards.
FTDI Viniculum FT90x stuff. Hmmm, not familiar with it...yet.
I would steer clear of any of the FTDI uCs. Both generations of the Vinculum chips were awful and have soured me to their uC designs. Support for the Vinculum chips was terrible. Tons of weird bugs in the toolchain that never got fixed. Examples didn't work. FTDI refused to document the internal architecture or peripherals and you had to access everything via buggy libraries they supplied. There are lots of complaints about these chips online if you search.
That said, the FT90x does appear to be a newer design and isn't a Vinculum as it is now 32-bit instead of the 16-bit core in the Vinculum. It does appear to be documented better and the FT90x user manual lists register maps etc... FTDI spunoff a new company called Bridgetek to handle all of these chips.
Up to you to decide but I wouldn't...