The Mean Well looks like it's designed to drive another driver downstream. Fixed voltage in this circumstance won't help you.
For driving multiple XM-L's Mean Well makes a whole pile of AC drivers in the 2-3amp range. Not sure where to start.
For DC/DC applications looks at some of the flashlight drivers on Kaidomain or DX that Purduephotog mentioned.
I found a cheap source for AC-DC adaptor with 3.3v 2.5amps output. I think those are produced for network router which is quite a good candidate for driving a single XML without much complication. Will be testing it once I receive the shipment.
For DC/DC application, there's a chip call GS6300 (http://www.shoptronica.com/images/GS6300.pdf) which is capable to provide constant current up to 3amps with input from 4.5V to 40v. Any electrition which is good at the diagram and provide a simple guide on resistor required for 2 & 3 amps ?