Tube rolling on PrimaLuna P2

I recently purchased the PrimaLuna Prologue Two and I am interested in trying my had at tube rolling. Any suggestions? What can I expect from 6550s, KT90s. The unit sounds pretty darn good with the stock KT88s, not that far off from my YBA Integre DT.
Not exactly on point but....I have the Prologue One and have played with tube rolling for three months. The bottom line....the stock tubes were excellent and the replacement tubes I ended up using were not that much better sonically than the originals. I probably would/should have been happy with the originals - I was just curious. What I did learn of importance was - I have 4 ohm speakers and I assumed they would sound better connected to the 4 ohm tap. This turned out to be the cause a raggedness in the uppermids/highs that I had initially attributed to the tube complement. Connected to the 8 ohm taps, with the exception of a very little bit of softness in the bass (my speakers are cacaple of very tight bass) the raggedness in the upper end disappeared. Just something to consider before you embark on tube changes.
Newbee, you didn't use NOS 12AX7 tubes though, right? You used EI 12AX7s. Did you try any other tubes? I have the Two and I'm thinking of trying some Mullards.
Plinko, Short version - I ended up using some NOS short grey plate EI's I had on hand in combination with some Svetlana's of which I have a "lifetime supply" (so it seems). Very full and dynamic yet retaining smoothness and clean clear mids and highs. An excellent combo.

I also tried current production EH's (the best next to the NOS EI's). The new EI's - very clean clear mids and highs but a bit lacking in the bass which made them seem a bit bright (but I love them in 2 of my DAC's and another pre-amp), JJ's which were too full in the bass and not as smooth in the highs, and some Sovtek LPS with which I just made no connection (but these were 4 years old, I don't know about the latest production which I have heard is quite good. I also tried some NOS Chinese very low noise tubes which were too rolled off with the Svets, but which I want to try some time with NOS EI EL34's and E34L's I have on hand. I think that has potential for a good combo.

As it is right now I'm running NOS EI12AX7's, NOS EI12AU7's and Svetlana's.

Can't comment much on the Mullards in your amp but I would probably think twice before i would invest money in seriously expensive NOS tubes until you have a fix on the tonal quality you need in your unit, which could also depend on the power tubes you end up with. Personally, I'd be concerned that the Mullard might be a bit too warm for either of our amps.

Have you or are you going to fiddle around with power tubes? I'm not a big KT88 fan (only from experience in three different amps I have) and admit I'm a bit curious to hear the PL2 with 6550's (like Svet's (SED's) which I use in my main amps. Let us know how your tube experiments go.
oops, I think I remembered a previous post from you incorrectly or just assumed the EI's were new production. sorry! Yes, I plan to try power tubes but first I want to try some 12AX7's and the the AUs. I agree, 6550's would be the ticket. Although, it is probably going to be a year before I get around to the power tubes.

I was thinking Mullards because I tend to think that my speakers (Axioms) are, if not neutral, perhaps lean towards bright. If were overly critical and in a bad mood, I might say that. I actually don't think the amp with the stock tubes is anywhere close to being too warm. I never did find out what tubes came with the unit.
Plinko, did you ever get around to trying Mullards in your Two???
Yes sir, I sure did and I like them a lot. Highly recommended. I also put in some Amperex 7316s and this gave a more energetic feel to the music. You can't go wrong, really. I liked this amp with the stock tubes for that matter. With the Mullards and Amperex's, everything is more precise. Tonality is better with the Mullards.