Which Audiologic dac was the first to go 24 bit?

Rcprince is correct.
I'm keeping my M34 DSM in original form (except for special tubes) to me it sounds absolutely fantastic,
(mine was Jerry's own personal unit a while back)
Newer is not always better, just different, sometimes worse, depending on ancillary equipment & preferences.

The difference in sound was not really that much at all, and Jerry told me that before I made the switch; I only did it because I expected Classic Records to release a lot of great DADs (which they didn't) and because I liked the Purcell upsampler (which I still like, but after taking it out I think it added too much noise to the signal and lost some of the AL's delicacy) which could output a 24-bit signal. Unless you have a source that sends out a true 24-bit digital signal you're better off with the 20-bit chips, which Jerry apparently felt were very good. In my case, the 24-bit chips still are a plus, because I am friends with a couple of recording engineers (one professional, one amateur) who have 24-bit/96khz machines, so I can listen to their master tapes through my unit.

I don't think he's going to install the 20 bits. If you guy's don't know, the Altis is a Bitstream machine.

Rx8man - Hello - your comment about "special tubes" caught my attention, as I have been wanting to try another set in my M34 dsm, purchased here used a couple years ago. We will be moving shortly; so, while the system is taken down, I thought it would be the opportune time to install new tubes, since I have no idea about the previous history of the stock unit. Also, my owner's manual apparently is missing the "tube placement diagram" page. I've never purchased a tube in my life, but figured I would contact Andy at Vintage Tube after reading about him here on the forum, and then at his website. Would you be willing to share your "special" ingredients.
Thanks very much for any suggestions you might care to provide.
Best regards,
Tom

Pat (Rx8man).....do you want to talk about tubes
in the M34, or do you want me to jump in at this
point?