I have a Stiletto I. I have tried several tubes and swapped them in and out in almost every configuration. First off, you are right to look at swapping out the stock Mesa tubes. I am always disappointed with the sound of the Stiletto with Mesa's tubes in them. Anyway, here's my findings.
1) JJ's high gain kit from Eurotubes. 5 high gain ECC83S and E34L power tubes. These were a significant enhancement to the stock tubes. I love Eurotubes customer service, prices and shipping time. They are good to deal with. The tubes on the other hand have a few drawbacks. The quality is not all that great. I had one of the preamp tubes blow out within 3 months. I also noticed a TON of hissing and microphonics from the tubes. I also lost control of my volume and gain knobs with them in. I couldn't turn the volume without them going from low to LOUD! My gain knob had no more control as well. This only happened with the JJ's in them. I don't think these tubes were a great match in my Stiletto. I put them in my Mark IV and they sounded great. So I'm not knocking them, just not recommending them in this amp.
2) Electro Harmonix hi gain rated 12AX7's. Terrible. Not good in the Stiletto. I put it in V1 and had even more hissing and loss of distortion than the JJ's. I got my knob control back, that was the only plus.
3) GROOVE TUBES. Let me say it again, Groove Tubes. Not only did I receive lightning fast delivery, 1 day. But I also got a TON of advice from Myles Rose (Amp Tube Genius!). There are so many things to think about when retubing an amp. It's overwhelming if you don't have a clue. Anyway, he educated me on exactly what each preamp position does and why it is so critical. I was going at it all wrong with the other tubes. Dah! Here's the thing, Groove Tubes have the STRICTEST quality control out of all the tube distributors, they also have the best and most accurate equipment in testing. They seek out a tube that will match your amp the best. Now, all this comes with a price. However, if you want the best sound, get the best tubes! But here's a secret. You do not need to completely re-tube your amp! All you need are 3 preamp tubes. V1, V2 and MPI. All you need to do is buy these 3 preamp tubes. If you REALLY want to you can buy new power tubes. However, these are the biggest change in tone to your amp. I did this for my Stiletto and got the Marshall SAG hi-gain kit. My Stiletto sounds PERFECT now. I really got my Marshall-like sound now. I have the control in my knobs with an incredible distortion breakup from my tubes. I will always get Groove Tubes from now on out. I did the same with my Roadster and got an insane amount of gain and response over the stock tubes. Beautiful.
If anyone has had a bad experience with the sound from Groove Tubes, I really believe it is because they got the wrong ones from them. There is a huge variety from Groove Tubes and if you buy a Russian tube when a Chinese tube would be a better fit, and then top it off by putting it in the wrong position then you will not get optimal results.
