by carlaz » Mon Jul 23, 2018 4:01 pm
If I remember correctly, the 4x12 Modern M 1-3, the 4x12 Vintage M1-2, the 4x12 Metal F1-2, the 4x12 Metal T 1-3, and the 4x12 Metal V 1-3 are all Amplitube 2-era cab models, from back before the software modeled the individual placement of different microphone models. So, originally, each of those cab variants were intended to model a complete cab mic'ing setup in a given space, with some (unknown) microphones placed in certain (unknown) positions.
So, yes, in theory, the 4x12 Modern M 1, M 2, and M 3 "cabs" all model a Marshall JCM800 4x12 cab with Celestion G-12T-75 speakers, just with three different mic setups. So, really, the above-mentioned cab models from AT2 are still available for backwards compatibility. To use them as intended in AT2 bu in AT3/4, you would presumably have to bypass the current mic/cab/room modelling part of the signal path.
The simplest thing to do is probably just treat them as "alternate" cab models. After all, it's not like every cab will sound the same as every other cab of the same make and model after 20 or 30 years of use and abuse.