Last summer our musa basjoo produced 5 stems.  These 5 stems were all a foot or two from where the main plant had grown the year before.  But that main plant did not grow last summer (rotted and died the winter before last).   So all 5 of these I guess are pups of the original plant.  Last fall I cut the 5 stems off about 5 inches above the ground and covered with a foot of oak leaves and pine straw.  I uncovered them last week, April 6, and it looks like all 5 stems survived and are growing. (see pic below.  normal brick for scale )  So my question is, can I separate them and transplant some of them elsewhere this spring? If so any tips on how to do it would be greatly appreciated. Or do I need to wait until fall?

You can transplant them.   Bananas produce Pups.  Just make sure the Pups have rooted and have gotten at least a foot tall.  Separate them from the mother or each other cleanly(don't rip them out) and preserve the roots.  Bananas do better if not crowded upon themselves.

jimmyt

No problems transplanting for sure, just be sure you get lots of roots when you cut them up like Jimmy mentions. ..i myself might divide the clump into 2, ..one w/ 3 pups, the other w/ 2 rather than separating individually.. less risk if something goes wrong.. would have an easier time getting established as well. I might also let them put on a little more growth beforehand.    
   Beyond that, def. wouldn't wait until late summer / fall since you want the plants to get themselves somewhat established while it is warm. This will give them a leg up once it starts getting cool /cold there later on. Less chance for any possible issues come next winter when they go dormant again..

Yep, I agree with the others.  I'd let them get a leaf or two going and then dig around them to separate them.  Go in between them with a trowel so you can slice them off cleanly.  Like Silas said, you could leave a few in place in the existing clump, and separate a couple for transplanting.  Pups usually grow pretty quickly if you give them rich soil and a reasonable amount of water.