If you plan to use an ATC, then tension/compression is the way to go, rather than a tapping head, as the tapping head cannot be used in an ATC.

BTW - On the Procunier, make sure you KNOW the true spindle speed, and set your feed rate based on that, NOT the speed you command in Mach3. Unlike other tapping heads, the Procunier does not tolerate the spindle down-feed exceeding the advance rate of the tap. If the head tries to lead the tap, the tap WILL be broken. Even knowing the actual spindle speed, I would suggest under-feeding by perhaps 5%, just to be safe. The Procunier will modulate its clutch as needed to feed properly.

Regards,
Ray L.