each 12V rail is capable of 40 amps, but not simultaneously ... that PS cannot handle 160 amps
the total rating of the PS is 750W ... ignoring all else that equates to total of 62.5 amps at 12V
you may be ok if you are only needing 10-12 amps per MR 16 (I like to leave some margin, plus some power will be used elsewhere) ... otherwise I would suggest multiple power supplies