Audible Illusions M3a preamp

Question for any and all M3a owners??? Anyone know the year the last factory "mod/update/upgrade" was done to this unit, so one knows if he has the latest greatest M3a??? Also, mine was purchased as a "factory refurbished unit" & came with the Russian 6H23nEB tubes in 2014, system includes new Aragon 8008( Indy Labs), Linn LP-12, Ittok LVII, Van Den Hul MM-1, Marantz UD8004 Blue ray, & Maggie 1.6's. Question/opinion even if my M3a is the "latest greatest", would the cost of moving to a M3b make my system that much better???  Thank You Kindly
As a 24 year AI user, I would say it would be comparable to the difference in stepping up from a 2D to a 3.  This is going by what AI says and what I've read.  I have no actual experience going from a 3A to a 3B.  I've had a 2D and a 3A which I still have.  The 3 to a 3A might have been the biggest difference up to now.
I had a 3A and now have the 3B.  It is night and day difference.  The switching is now done by relays and the noise floor is much lower which makes for a much quieter preamp.
Any ideas of cost trading up to the M3b going direct to Audible Illusions??? Has anyone done this or gone through a dealer??? Any response is greatly appreciated.
call gcaudio ,texas talk to galen carol
AI offers a trade up policy.  Depending on which version of the 3A you have will determine the trade in value.  Call AI with the serial number of your unit and they will give you the trade in price.  The later models of the 3A are worth more than the earlier models.
Audible Illusions continues to experience long delays in delivering their products. I ordered an M3B in late December 2015, the final payment was solicited (and paid) in late January - when I was told that the preamp was "on the bench" by Jerry at AI. The only thing on the bench, as far as I can tell, was my cash. I feel like I am getting the run around everytime I call AI. I just called AI for the 6th time since ordering the preamp only to be told that they are out of tubes and are waiting for the delivery of Swiss switches and that they have no idea when they are coming in. "But don't worry you will get your preamp soon." I miss dealing directly with Art Ferris who is a heck of a nice guy and a straight shooter ( as well as and audio engineering genius). I've happily owned a Modulus 1, 2 and 3, but I am very close to demanding my money back and buying from the competition.   I hear the PrimaLuna DiaLogue Premium Preamplifier is pretty good.