Well roomie most likely has component libraries of IR commands that you just assign to buttons, but the native command actually being sent to the iTach looks something like this:
sendir,1:3,1,39000,3,1,95,23,48,23,48,23,48,23,48,23,23,23,48,23,23,23,23,23,48,23,23,23,48,23,48,23,23,23,48,23,23,23,23,23,23,23,48,23,48,23,48,512\r
The above command is a discreet ‘off’ command for a Sony BluRay Player. You can find these commands online in various formats, and GC has a conversion app to convert raw HEX to native GC commands. Also, your iTach has the ability to record these codes directly from your IR remotes using the iLearn app they provide.
Once you know the codes you want to send, you send it from a SmartApp with the send hub command I previously described here.