Hi Reggie,
I also use an AT OC-9 ml ii and like you used it with an AT-630. I also tried various other SUTs including the AT 650, Black Head, RFC and probably some others I have forgotten. Recently I stumbled upon two much better solutions. One being the Puresound T10, the current model with the 2 gain settings (the older model with 5 settings was no good with the OC-9). Second solution is a Denon HA-500 head amp. Both these step up options make the oc-9 sing with plenty of energy and presence. It sounds like a much more expensive cart.
The Denon has more leading edge attack and openness at the expense of a bit more surface noise and the T10 is a little smoother. Either are excellent and transform the OC-9 into a seriously good cart.
Graham