No sorry I do not have the S530's, I do however have the Z5500's but not sure how much of a comparison can be drawn from them.
The Z5500's are indeed 5.1 they are also 500w and use a huge sub which produces quite a decent amount of bass. They are not audiophile quality and the satellites will distort at higher volume levels, but for the price they are pretty good. I use them for everything including music but the are better for movies or gaming.
Funny enough I am also contemplating a decent set of 2.1's or components to replace the Z5500's, I'd prefer something a bit smaller with a bit more clarity and just use the Z5500 as a home theater set up.
Would be interested to see what you end up getting.