I own a Triaxis and want to sell it.
For many people it is the best preamp ever. Not for me.
It has nice metal sounds, very tight and it is very versatile in case you want different tones for different styles, but I came to conclusion that I don't like Mesa Boogie, not even Dual Recto, I'm going to switch to Engl and probably buy a E570 (E530's big bro).
I find Triaxis a bit weak and thin in some mid low area frequencies. Not ballsy enough. Somebody told me that is just a matter of tubes... actually I have tried EH, Sovteks and TungSols, and not big improvements.
I also think Triaxis is a great preamp for soloists but not for rythm power riffings. In the mid 90's most of the shredding geeks had one.
Another thing you probably should know is that it is recommended to match it with the mesa 2:90 poweramp. That is fucking true. I used to play it with a Peavey 50/50 and some months ago I got a 2:90... tone improved a lot, much richer, specially with deep and Modern modes on.
So, after 3 years i will sell it. If I had money I would keep it with me forever.
Very good for classic metal and shredding. Reliable on stage.
Not so good for modern metal.