From my testing I do not believe the control port is TTL compatible even on the new 2.4G TTL flashes. TTL information is only transmitted through the flash foot so the X1R-C receiver would be needed for using your v860c in TTL with the X1-C. I have tried using the XTR-16s receiver on the TT685c and could only transmit Manual flash power settings with the X1-C. When the flash and the X1-C were both set to TTL I got no response to any changes to FEC in the X1-C and the flash exposure was way under exposed. I changed the FEC directly in the flash as well but the flash exposure remained the same. Even with both the flash and X1-C set to Multi mode I had no control of even the Manual flash power setting let alone having the ability to set the number and frequency of flashes from the X1-C. I could how ever with the flash set to Multi mode, change the flash power in full stops, when the X1-C was set to Manual flash mode. So I deduct that the only real control of the X1-C, through the XTR-16 receiver, is for Manual flash settings, in only the Manual flash mode and for triggering. I guess you could use the Multi mode as well, in a setup as I described above.