Christmas Cactus

I feel it is time to put my two Xmas cacti in larger pots. They are still in the 3" pots from K-Mart when I bought them before Christmas. They were full of blooms but when I got them home the blooms wilted and fell off. The plants, though, are growing by leaps and bounds. There appears to be "strings" coming out from where the leaves section together. It's all over both plants so I am assuming this is normal. I know enough that it won't be good to do this in regular potting soil -- do I use just the special cactus mix I got at Home Depot that I used for my succys? I noticed yesterday that one of them had lost some leaves so I watered the poor thing. Every other houseplant I have has been overwatered so was I surprised to find these were completely dried out. Thanks guys!
Chris, TN Z6

I think those "stringy" looking things are rudimentary roots of a sort, or possibly what passes for "primitive" spines , typical for most cacti most likely?? Mine do the same thing! Often it's a sign as well , that the humidities are sufficient for such root growth and grown under drier air conditions you don't get many of them!

So that is good?? I can go ahead and repot?