I think you need to have dedicated resource calendars for TMSXE, I've always used new calendars meant just for TMSXE. If you use existing resource calendars, I believe TMS will try and schedule a conference for any meeting that already exists on the calendar, but I'm not 100% sure.
When scheduling conference in TMSXE, the meeting owner will receive an email confirmation from TMS, the owner then must either forward that to other attendees or paste the contents of the confirmation email it in the existing meeting invite.