I used two vibes because it is technically impossible for one player to handle it.
Could be, Larry, could be -- parts of it are fairly busy, and that depends on a number of specific factors of reach, spacing, etc.
I went to school with a fellow years back, though, who routinely did fairly quick Bach four-part organ literature on the marimba. Admittedly, an outstanding player... but the stick instruments (and their players) are often underestimated!
Awesome! I love it! Hmmm... I can't decide which one I like more... Well, just don't ask me to decide and I'll be fine. The marimba version was certainly worth creating though. Great work as usual! My ear is hearing some good vibrations...