Wow, that Propeller thing is... unusual*.
The propeller claims to be able to do 40mA per pin, you can probably do it by just putting a ~330Ohm current limiting resistor in series. If you are having trouble, consider putting a buffer in between.
You can see how the digital sidecar buffers its signal on page 3 of
http://usfirst.org/uploadedFiles/DSC...matic%20v7.pdf
Then it is just a matter of creating your PWM signals, which should be relatively straight forward.
*
This document was my introduction to it. Wow.