Qavion - I think you're right that TAS comes from the ADCs (CAS corrected for altitude (pressure) and temperature (density) errors). TAS is only displayed in the FMS, on progress page 3, not on the flight instruments (its not really much use on its own except for flight planning maybe). However, to get the wind vector on the EHSI, the IRSs compare TAS with GS, and HDG with Track. Hope this helps.
GS is displayed on the EADI in the bottom LH corner next to Mach Number. Also can be displayed on the IRS overhead display.