Use Combi mode to record multi-timbral sequences by assigning different MIDI channels to the programs that make up the Combi.

You cannot add samples to a stock M1 from your PC.

You can up/download Programs, Combis, and Sequence data using a sequencer which allows sys-ex dumps (I have no idea if you Cakewalk demo will) or by using a dedicated librarian. Using an editor you can edit Programs much easier. Try editor/librarians for the PC at:
http://ciarm.ing.unibo.it/researches/m1/index.html
http://www.geocities.com/SiliconValley/Way/5891/index.htm