Having to piece together the units’ gives the option of getting what you want. There are speaker systems with 5.2 or with 3 subs for that matter. However, more subs are harder to setup. I had two subs setup one time and it’s nice. If you get a complete system, you don't have to worry about piecing together the system. And you'll probably have to spend the cash all at once, while if you piece them together; you'll stop until your heart content or until your pocket runs dry.
One of the most important equipment on your audio system is the amplifier, so pick one that you can live with and then base the speakers you'll get from it. Most cases though, you'll like not need a second sub if you are getting a full range floor standing speaker system. Picking up which brands/system is a matter of personal taste and budget and how you use the system.
I suggest you try the amp and speakers before buying because that's the only way to know if you get what you want. Links below are some of those small business operator who makes very good speakers and take pride of their works, which you probably knew already.