flyfly4, if you do the "AQC" with CTC and you meet the required standard during the course, then you will go into their hold pool. Then when you're near the top of the list, and you meet the requirements specified by the airline, they will offer you the chance to go for selection for that airline.
Whether you do ground school or not with CTC is irrelevant as far as I know.
Points to note - Doing the "AQC" does not automatically guarantee an interview... if you fall short of the standard, you will not make it into the hold pool and therefore will not get an interview.
The aviation industry changes pretty rapidly, and what is the case today, may be different next week.
There are many people doing an MCC/JOC at CTC having already done one previously. Several of them did one at Simtech, then only a couple of months later went to CTC as well. Several at my airline have done more than one MCC/JOCs, and went to CTC in order to get better access to the jobs and opportunities.