EAR 834P tubes: which to match?

I'm upgrading the three Sovtek 12AX7 tubes presently in my EAR 834P phono preamp, and have no circuit diagram (not that it would help me much if I did), and don't know whether all three should ideally be matched, or whether just two of the three should be. My guess is that the outside two should match and that the one in between them need not match them--but that's really just a wild guess.

Does anyone know the answer to this?

I've just finished putting the 834P and a pair of Shallco-Holco ladder attenuators in a wooden chassis, with wires going from the 834P's output jacks to "In" on the Shallco switches, and from "Out" on the switches to output connectors, from which I go straight into my monoblock power amps, cutting out a separate preamp (active or passive) and the cables and connectors it would entail. I can hear a clear improvement in quietness and transparency.
This has nothing to do with my question, but I can't help telling everybody about it these days--sorry!
I have often wonder, having been in the same situation before. Anyhow, here you could talk to the US distributeur 562 422 4747
Come back here to write your own answer to your own question for the rest of us.
The tube closest to the front of the 834P will make more difference in the sound of the unit than the other two. You can use a 12AU7 or equivalent as a substitute for the 12AX7.

The two tubes closest to the back of the unit control left and right gain and should be matched if possible. ONLY 12AX7 tubes should be used in these locations.