The FT command is not currently supported in the 1.10.8 BETA. It will be supported in the next public release. However, there is a major caveat. When using the Kenwood command FT, the underlying assumption is that there is only a VFO-A and VFO-B and hence the command will only respond with the argument of 0 (VFO-A) or 1 (VFO-B) as the transmitter. The FLEX-6000 can assign the transmitter to VFO-A thru VFO-H. So if Slice C-H is the transmitter, the FLEX-6000 will respond back with the FT0 (VFO-A).
This will work fine as long as you are emulating a legacy radio by only having Slice A and Slice B active.