I have used the Dektec ASI output and modulator cards for many years. Playout data loops for updating/testing STBs and audio files for radio via satellite.
Have bought several cards on Ebay for under $100, but usually they don't come with a license and those are not cheap! Did you get the license with yours?
You could also purchase a PCI modulator to directly output a signal (your choice of flavor) from a TS instead of outputting ASI to an external modulator.
Yes, you could injest TCP or UDP streams instead of TS playout.
Brian Gohl
Titanium Satellite