Well since I have the first modded V3 as well as it being the ACM mod I have a bunch of thoughts.
First and foremost I want to let it be known that the mod is NOT for all mics. I did not like it at all with either my AKG's (480) or the Neumann 140's. The 140's worked alot better than the 480's but they still weren't perfect. Currently i've been using it with my Neumann midside setup and it sounds great. I'l run it with the DPA's next week for Mule and Panic.
The mod itself ONLY affects the a/d chips within the unit. Nothing on the preamp side is touched thankfully. The biggest thing that comes to mind when I think of the sound is "big soundstage". Really a huge improvement. I've found that the sound also tends to be more in your face than stock. The big soundstage sound takes away alot of the sterility of the stock a/d section.
For a good example orechall ran my ACM V3 this past weekend at Panic. 4023 > ACM V3 > 722. I've only heard the first night so far but I honestly think that of all the sources out that his are the winners. Lots of other great sounding tapes but his really do standout.
I'd be more than happy to answer any specific questions if you have nay about the mod.