I associate a larger soundstage with increased resolution, always a good thing. I've never heard a too large soundstage, unfocused yes, but increases in depth, height and width have always been positive, the amount of immersion/forwardness can be exasperated by a larger soundstage.
You mention increases in detail, openness with the XLO,based on your description I think it is likely the MIT is failing to reach the full potential of your system in regard to detail and soundstage. I wouldn't give up on the XLO just yet.
Seems you're suffering from an unfocused, forward soundstage, you don't mention height, width and depth being a problem. Your problems with the XLO could simply be exposing issues elsewhere in the system. I've found different isolation schemes can help focus to a large extent, get your equipment off any compliant devices, use spikes and ball bearing devices. You also may have to try different cabling in the rest of your system in order to reduce forwardness. It could also be the XLO will never be synergistic in your system, still, I wouldn't give up on creating a larger soundstage. You can have focus, proper perspective and a large soundstage all in correct proportion, may take some work!
