I would stick with montipora caps and digitata. If they do well try a few acro frags. Over the past year I've come to realize that water quality is more important than lighting for keeping SPS healthy and colorful. As for the LPS, I don't think you'll have problems at all with that lighting
Unless, of course, you keep it in a cube tank that has a 30" depth, then you may have some problems - depth to the lights is also an important factor, alsthough I have stuff living quite nicely under rocks with little light (go figure).
Monti's all the way, but pick up the slack in water quailty as you dont have light intensity as a cushion.
Some LPS require high light, such as closed brains, favites most LPS will do fine under PC's though
Worst case scenario with low lights for montis is that they lose their color (brown). I have never heard of one dying from lack of light (unless they were in a sump or under a rock).
Water quality is much more important.
Seems to be same for xenia as well. Xenia on the bottom of my tank do about as well as the ones at the top.