I don't know if these generalized, uneducated, subjective comments will be worth much to people but here they are. I don't know how to tell which cabinet is actually flatter. If anyone can suggest something useful that can be done with the Behringer reference mic in this regard, I have one.
At moderate and high volume levels or commercial music, the Alto seems to have more forward midrange compared to the EV. The EV lows may be exaggerated a little bit while the Alto highs may be subdued a bit.
In switching back and forth with recorded tracks, neither cabinet sounds particularly harsh or fatiguing but the EV sounds "richer"- even against the alto with the "contour" switch engaged. This is with the EV set to flat/full range. The alto sounded fine to me but the EV just sounded more detailed.
I hadn't previously gotten on well with the EV for axe-II use. I spent a while working with IR's on the Alto and found it easier to tolerate than my past efforts with the EV. I suspect that the higher crossover means that more of the sound is being produced by the woofer and maybe that helps but it could just be mental silliness. While I didn't "love" any of the IR's I tried, I was able to play without feeling the urge to just quit and throw the monitors in the trash like previous times.
The surprise for me was when I switched back to the EV and this time it was workable. My buddy and I both thought the EV sounded somewhat better than the Alto- a little smoother perhaps. In listening to music, the Alto seemed to have more obvious midrange and perhaps this makes it sound a bit more "forward" with the axe-fx.
Both units have dual inputs so that they can perform a basic mixing duty. While the alto just has a level control for each input, the EV also has an overall level control. The alto has a built-in fan while the EV does not.
One thing that always bugs me playing guitar direct is the sense of a "metallic" overtone compared to guitar cabs. I don't really know how to explain that and I doubt I could illustrate it in a recording. I don't know if anyone out there could relate to the "metallic" or "hard" description but if anyone has a suggestion for reducing that, please feel free.
If anyone has questions or suggestions in general, let me know. I'm not sure if I'm going to pick up the second Alto and/or return the EV yet.