This note is mostly FYI for Redbus. I am sad to report that it appears that with OS X 10.10 Developer Preview Seed 4 that was released today, the IFFW drivers are no longer working or recognized in Audio/MIDI Setup.
Verified issue on a new Mac Pro and older MacBook Pro. Was working ok with Developer Preview Seeds 1, 2 and 3 though I only did minor testing with Preview Seed 3. It's getting late so I have not looked into to much further other than trying to uninstall and reinstall the F6 drivers but it looks like Apple is now enforcing the requested migration for developers to adhere to the new 10.10 Yosemite User-Space driver protocol.
TCAT and/or Tascam may need to get their hands dirty to resolve this.