You are sure to get plenty of recommendations on here. However, few will be of any unique value, if it goes anything like it usually does.
I will, however, make very informed suggestion, based on thorough knowledge of measured behavior vs. human perception(as established by the credible research in this field). Look up my posting history if you must.
I recommend a full set of the Behringer B2030P as your L, R, C, SL and SR. There is no retail speaker that I know of that can compare, overall, in the critical measured parameters, that will come anywhere close to the price.
The B2030P is $130 per pair. It is a passive studio control monitor. It is superior to most bookshelf speakers, measurably(in the most important areas), overall, that cost upwards of $1000/pair. Not my opinion - this is observed data that I am merely commenting upon.
The B2020P should have basic mods to fix a few mass manufacturing issues(that are common on many speakers). These are very easy mods for anyone, such as: dab some super glue on a part inside to prevent it from vibrating and putting a little rope caulk between two joints to prevent an air break/leak). If you take care of these basic issues, it will be a speaker that will be difficult for you to 'upgrade' from unless you spend a considerable amount of money. The Paradigm S1 is a speaker that could classify as a considerable upgrade. At about $1500/pair, you have to spend more then 10x the cost of the Behringers to achieve this significant upgrade. The S1 has certain physical parameters that will allow it to exceed the Behringer in audible sound quality - primarily the cabinet on the S1 - which is a solid cast alloy metal with dense cast bracing - resulting in lower cabinet panel output coloration. The dispersion, also very critical, is unusually superb on both the Behringer and the Paradigm S1. The Paradigm will have slightly better overall dynamic ability when pushed to it's limits.
For the subwoofer, that is another issue. But you should use at least 2 subwoofers to get the best/ideal integration that is seamless between the Behringers and the subs.
-Chris