The first thing we have to determine is whether you have MTS Classic TV or MTS Ultimate. MTS Classic uses one dark coloured STB for the whole house; MTS Ultimate is newer and uses a mainly silver-coloured STB for each TV. In either case, the computer tuner will be tuned to a set channel and the actual channel changes are done by the STB.
If you have MTS Classic and you want to use your PC for recording TV, I would suggest you consider upgrading to MTS Ultimate instead which includes a PVR. If you want to use your PC as an extra TV screen, tune the PC tuner to either 4, 8 or 11 and use the corresponding remote to change channels.
The IR blaster that comes from MTS is used to control a VCR that is adjacent to STB.