I believe you may be headed in the wrong direction if you're seeking "more warmth". I own Premier 12's and pair them with the Premier 16. I've also owned the CT6 and extensively auditioned the CT5. Of the 3 preamps the 16 is by far the "warmest" (and best pre, IMO).
Knowing that the PV12 is of the same vintage as the 16's, I think the warmest pairing would be the PV12 with the Premier 12's.
Knowing that the PV12 is of the same vintage as the 16's, I think the warmest pairing would be the PV12 with the Premier 12's.