Agm,i you get a passive pre-amp or TVC with a XLR out to A21, you will have more than enough gain in the system. The reason is that the 2.4V from the Quad CDP will be seen as 4.8V on XLR to A21. This made a HUGE difference in dynamics in my system. If you do not intend to go XRL between the passive preamp or TVC and the A21, then I would suggest you to avoid the passive preamp or TVC.
I have no idea on TT and what how much voltage it sends to the preamp. Good Luck in your search.
I have no idea on TT and what how much voltage it sends to the preamp. Good Luck in your search.