I believe that the THX navigation for the TC was nearly the same as the THX navigation for the LS. You would also need the DVD map drive/brain that goes in the trunk, a DVD map disc, the GPS antenna (goes in the dash), a different rear view mirror (has the microphone for voice commands), a four channel amp that goes in the trunk (the unit can't drive any speakers directly), if you don't already have subs and a sub amp, you'll need that too. You will also need a lot of wiring harness (between head unit and trunk unit, between head unit and amp in the trunk, between head unit and mirror, between amp in trunk and each door, ...), you may also need new button pods for you steering wheel.
It is way, way easier to go aftermarket, and that way you can get maps newer than 2012. (The last maps that came out were in 2012, but were already out of date by two years or so.) You can get aftermarket that looks as good as factory.