This is an LED driver controller. It will not drive leds directly. It can control multiple drivers with each channel running independently of the other.
A driver capable of running 20 xm-l's in series would be out-puting over 90vdc to do so. That's a crazy amount of voltage to be playing with in a DIY led build. I doubt many companies would produce a driver with such extreme output specs for DIY use, though I have seen voltages that high in some of the cheaper chinese led fixtures.
Actually there are several companies that produce some wicked-large LED drivers, I've seen (if I recall correctly) Meanwells and Thomas Research drivers that go up into the 100-200v range (DC output).