Hi, for us to really be able to help you'll have to specify exactly the firmware versions you installed, plus exactly the Camera System / Flash system settings on the Tx unit, plus the Flash System settings on the Rx units.
They are both P-TTL flashes (I assume), so the Flash system should be "Pentax", but as ClassA said earlier you have to manually choose the flash itself. If a specific flash is not listed then I think you have the option of "Auto Pentax" to try.
If you are running the XTTL firmware then on the Tx your Sync Mode setting should be on "Normal HSS" (in the Functions menu).
BTW, a quick check on the Cactus V6II webpage compatibility chart :
"Pentax
P-TTL The following flashes are not supported:
- Sigma EF-610 DG ST for PTTL"
But you have the "Super" version, so I guess that's OK .... its the one that has HSS anyway
.