My wife proclaimed that I must make the black boxes go away...

So, I'm going to use Paradigm AMS-100R (in-ceiling) speakers for my surrounds. Fortunately there is a chase which affords me access to run the wires up into the ceiling. It has open joists so it will be easy to use a fish tape to get them where I want it.

My questions are:

What is the difference between regular speaker wire and that designated for in-wall use? I've seen rolls of both 2 wire and 4 wire in-wall cable. I presume the 4 wire is intended for where there is only room to run 1 cable? How do you connect the two separate speakers from a 4 wire cable- do you just cut a slit in the cable jacket and pull out the two wires for speaker 1 and then continue with only two wires in the jacket on to speaker 2? As getting the cables up into the ceiling isn't really a problem, does it make sense to use 2 or 4 wire cable?

The total cable lenght is going to be about 40 feet. The cable I was planning on using is 16gauge. Is that sufficient?

Thanks for your help!