yes. even the ones that come into one muffler are still considered true duals. the flow chambers are actually still seperate inside the muffler case. imagine it like the one pictured below, with a big case around it.
i just did a little looking and the difference between akrapovics slip on system and the evolution system is that you will only get the muffler in the slip on, just as u implied above. it will bolt in place of your existing muffler and uses existing mounting points.
the evolution system is from the catalytic converters back. (cat back)
i can't imagine just the slip on changing sound (or performance) that dramatically since u will be using all stock other than the muffler
no systems will come with test pipes from my knowledge. thats something that will have to be purchased seperately.