I have a Triax TSS400 and TVHeadend does present DiSEqC options, and I believe it should work.
!wDiSEqC.png!
However in my setup I have three ports permanently connected to 28.2°E, and one port which is dedicated to 19.2°E (shown here as disabled as it's only placed on the patio on non-BBC Grand Prix weekends).
On my Sat>IP tuner there is an option to switch between different LNB types
!triax.png!
Once you've done this each input becomes totally separate tuner as far as the SAT>IP tuner and TVHeadend are concerned - at one point during my playing around I have one 28.2°E feed split between two tuners (TVHeadend takes care of the polarity and 22kHz tone), one 19.2°E feed, and a 13°E feed from an LNB blu-taced to the patio dish :D
However all the LNB's have to be the same type (i.e. Universal - you can't have a mixture of, say, Telecom, Ka, and Universal - or you could but the frequencies would be all wrong).
