Don't buy the cs10, you want to get the csi a4 or a6 because those are tuned to match your set (or another rti a1 if you can find a single). The surrounds don't matter as much but I'd stay within the same series if you can help it.
http://www.polkaudio.com/homeaudio/rtia/
There are a couple on ebay for ~150. Polk also has a great ebay store for their refrubs.
I also have a dayton sub 120. Personally it's plenty of sub for me and I don't plan on upgrading until it breaks (hopefully not soon). I'm not saying the others are wrong, it's just important to note that for some of us 150$ sub is enough and not just a stepping stone.