Difficult question to answer without knowing the current sound characteristics in your system (warm/dark, too detailed and dry, slight brightness, lacking transparency and micro-detail, etc.)

There's lots of information on tube-rolling in the Mini-Torii forum section.  In particular, check experiences from Les Lammers.

Personally, I'm currently in the process of fine-tuning mine and so far I've some conclusions, but these do not stem from an exhaustive tube selection, just a particular stash of very useful alternatives.  There are many more tubes I could eventually try, but that's not the intent in my case. So, consider these suggestions as mere examples.

I would suggest to consider NOS 12AT7 for drivers (Tungsram, Brimar, Psvanes), current production reissue Tung-Sol 6V6GT's (great sound!), Reflektor factory NOS black glass Russian 6V6's (need some long burning in), RFT EZ-80 rectifiers (preferred, but RFT EZ-81 could also be nice).

The rest will depend on the sound you want to get, as stated earlier (from OA3, OB3, OC3 to OD3 output voltage regulators, for example), and OA2 (VR150) as opposed to OC2 (VR75) in the input voltage regulation, all these possible combinations giving you choices in terms of warmth vs transparency and bass profiles with the output regulation, gain modifications with the input regulation.

This, of course, is always system-dependent and YMMV.  You'll need therefore to try some potentially interesting tube alternatives on your own to have an idea where you stand/like and then fine-tune.

I'm not familiar with the 5881, but the earlier mentioned 6V6 choices are very good as well as the stock JJ 6V6 S (although to me, the latter is a little dull in comparison).  Reissue Tung-Sol 6V6GT's are just the best I've heard so far (YMMV).

Be patient, as you'll need some time to critically listen the various combinations involved and eventually fine-tune based on your own ears.  For example, Brimar 12AT7's (really long burning-in times) are not happy with the Reflektor black glass NOS 6V6's mentioned.  For these I recommend the 12AU7 variation 5963, as a better pairing (a smooth driver with nice low-end effect).  Brimars have better synergies with the reissue Tung-Sol or the stock JJ 6V6 S's.

Finally, if you are replacing the original tube complement just in grounds of reliability, the only issues I know of are with the JJ EZ-81 rectifiers, and not the rest, which have proven very reliable to me so far.

Good luck!

Thanks for the input guys! Glad to hear the only JJ's with issues are the EZ81's. You make a very good point... one must listen critically before changing the tubes out. Without time for adequate listening and break-in it would be impossible to really *hear* the music coming from the amp.

Does anyone know what the power tube plate voltage runs at on a mini torii? Thanks!

I can't use those tubes in my M-T though, correct?

I agree with Lon.  In my experience of 8 months with the M-T and after reading countless reports here and in other forums concerning JJ tubes in general, these are well made.  

Many people really mistreat the output types in guitars, for example, and they still prefer them for their ruggedness and sound, with the only caveat that they sound a little compressed compared to a few others.

Having said that, the recent history of early failures with the JJ EZ-81 is so evident, users now tend to replace them prophylactically, before that happens.  I'm not sure why Decware continues to ship them with the Mini, but given JJ's good reputation, I guess the expectation is that this is just a bad lot-related, temporary situation.

I would strongly recommend good NOS rectifiers for this particularly critical tube duty.

Jim McShane is leery of JJ octals.

I personally have experienced premature JJ tube death: a 6V6, 6922's (more than 1) and on the forums there are numerous tales of sketchy JJ quality control and failures. I am sure there are plenty of good JJ's out there, like Lon's E34L's; I even have a few JJ 6922's that are still good. But the failures are mounting and to ignore that seems unwise.

The new production Tung Sol 6V6 is an excellent sounding tube. RFT rectifiers are good and not expensive. Choice of an input tube depends on the rest of your system.

I've found in the M-T, using 6V6 exclusively, that the key is finding synergies among the driver (input) tubes and the output tubes, for a given listening room condition (mainly the speakers' interaction with these conditions and the sourcing's profile characteristics.)  

The rest of the tube choices can enhance or detract from this synergy, but at a lesser effect.  The exception of course, is the low-frequency profile impact that the OA3 ... OD3 series can bring to 'color' that synergy. These would make it lighter or darker (detailed or warmer), but won't interfere with the essential job the drivers and output tubes have worked out together.

Whether this structure will remain across other non-6V6 output tube alternatives is something I ignore, but suspect the same outcome.

An additional variable, essential in my case, but maybe immaterial when using large floor standing speakers, is the application of a Sub-Woofer.  You can get away with OC3/OD3 output voltage regulation (i.e., lighter, more detail-retrieving with much less low frequency profiles but tighter low-mid range bass), if you adjust your well-placed Sub at a cross-over in the 65-55 Hz range.  

All that missing depth can be more than compensated setting the Sub's volume accordingly, especially when the Sub is being fed by the M-T's Pre-Outs, as these impart the M-T's signature at line level.

Yesterday I paired the stock JJ 6V6 with Psvane 12AT7's and was shocked at how good the combo sounded. The soundstage was wider and deeper. The amp seemed more powerful. Sonics were harmonically rich, detail and texture...excellent. Synergy. When these JJ die I'll get a pair of the cryoed and tested ones on fleabay. As always...YMMV.