This is xcpointx quote on the subject from Mon Aug 29, 2005 8:30 am:
The TriAxis was introduced to the world in October 1992 and began with serial
#T0001. That would have been the 1.0 software version. In January 1993 the
version 2.0 software was introduced. That would have been somewhere around
serial #T1700. In 1997 around serial #T5000, all TriAxis were leaving the
factory with the Phat MOD was part of the software. The Phat MOD only affects
Lead One RED. It simply smoothes out the top-end of the Rectifier Sound making
it sound more like the actual Rectifier itself.
The "FAT" Mod
TriAxis' shipped after June 97 have the new Lead One Red as standard specification. So serial #'s below 5200 have the Lead1 Recto mod and above 5200 have the "Fat Mod".
This mod is a circuit change to mode Lead One Red. A kit is available, that will enable an authorized MESA technician to do the work. Look for one in your area, or contact MESA directly.
MESA advises that users test a new TriAxis at their local dealer to see if the new tone works for them, before having the modification done. If you are happy with the sound of LD1, you may not like the change. I believe this mod is for those users that don't use their LD1 mode often. This modification will expand their use of this particular mode.
The current tone is described as being "fat, (of course) singing soloing tones that are super smooth" The high-end has been tailored for more balance.
There are no other modifications available for the TriAxis. The most current software version for the TriAxis is 2.0. Serial #'s above 1700 are version 2.0. When you power on the TriAxis the panel lights will flash a "1" for Version 1 or "2" for Version 2.