First tube roll: Which to change?

Incredibly enjoying my first integrated tube amp, so of course I want to begin messing with it.
The tube compliment is as follows:
4 x 5881
2 x 12AX7
2 x 6922
2 x 12AU7
So which should I swap out?
Let the gates open, I await your suggestions.
I'd recommend the preamp tubes first (12AX7, 6922). The 12AU7's may also be used in the preamp section, though they could be used as drivers too. I've found that changing the preamp tubes of a tube integrated amp affects the sound more than changing driver or power tubes.

The best bang for your buck is the 12AX7 as this is the first tube that the signal sees
I am guessing you have an Onix sp3. I found also that the 12ax7 position has the most effect on you tonal balance and flavor of the sound. The sp 3 has enough gain to sub a 5751 in this position and some of these really sound nice. I really like the GE black plates in this tube. In the 12ax7, I like the Groove Tube 12ax7m, but these are really hard to get. These bring back some of the classic tube sound to the amp. Also, get yourself a quad of Valve Art 350B. These babies make this a different amp entirely.
IMHO, I would really suggest that you just listen to the amp for at least a few months to let it break in and to get some idea of how it sounds, from bottom to top, and how it images. Also, how quiet it is. Find out how it sounds at low volumes and also at higher volumes. How much detail does it flesh out at low volumes, for instance? Then, AFTER you know what it sounds like, can you then make any judgements about tube swapping. Just my two cents worth, Happy Listening, and congratulations on your new amp. Sincerely,
Sane advice from Audiogonifiles! ;-).
Listen to the amp for a few months.
This is excellent advice. How could I tell any changes/improvements without first knowing the characteristics of the amp in its stock form?
Thanks for pulling me back.
Actually I am really enjoying the music, and that is what this is really all about.
Thank you.
Listen for a few months? If you knew what was in store for you to improve your amp, you will not wait at all this long. After a week or so of casual listening to burn in the amp, you should be able to sit down for an hour or so with your favorite music and then try ANY of the tube sockets with a few different brands. Be prepared to be shocked that first time. This would likely take a few nights for each tube. Repeat the process for the other sockets as you acquire various brands for each.

I have a pair of amps that use a 12ax7, 12au7 and 6922 per channel on the front end. Changing any of these makes a significant sonic improvement from the crappy Sovtek, EI and Electro Harmonix stock tubes. From my experience, it rarely matters where the tube is in the circuit. Each of the stock tubes is causing destruction to the performance capability of that amp.

The result from this process for my current amps, was that the edgy trebles are gone, the dynamic contrasts dramatically improved (mostly from the 12au7 swap) and the midrange becomes very smooth (mostly from the 6922). The 12ax7 was a nice improvement in tonal coherency and clarity. All of these as a new set took the amp to a level that I suspect even its designer had not observed. It is very likely that you will achieve similar benefits with your patience, time and effort here.

And learn about various tubes types (with different model numbers) that can be used in place of the tubes in your amp. This knowledge can help take your amp to another level of performance as well.

Way cool.
Thank you.

What is the purpose of the Valve Art 350B?
What tubes would they replace in my amp?