It would be a wonderful addition to add a "Room" setting in the Cabinet part of the Stack section. That would free up the reverb to still be used as normal, but give more life to the sound, particularly with headphones (as per Will Chen's excellent suggestion). When using the reverb for a room sound, there is a slight modulation effect.
In essence, it's like moving the mic away from the cab to get more room reflections. Axe has this option (but I still didn't get the level of realism as with the KPA. Which is why it's gone, baby, gone. LOL!)