Suggested center for Polk R15 and Future Upgrades

how about a CS1 from http://www.newegg.com/Product/Produc...lk+cs1&x=0&y=0

then consider the Polk Monitor series as an upgrade path with a lot of "bang for the buck"
http://www.newegg.com/Product/Produc...onitor&x=0&y=0

Well it kinda depends on what you have planned for your future mains. CSIA4 is fine if you plan to buy the RTiA speakers to go with them.

If you plan to buy Monitor 60s or 70's then the CS2 would perfect. And you'll get more for you money buying the outgoing Monitor series, especially from Newegg.

If you have no idea what you want for main speakers, it doesn't make a lot of sense to buy a Polk center. What happens if you decide you want Energy towers, Jamo towers or some other brand? Then the center wont match.

here is a different thought on your upgrade....
Take your $200 (plus a little) and buy two Polk Monitor 50 towers http://www.newegg.com/Product/Produc...tor+50&x=0&y=0 or add a bit to the budget and get a pair of Monitor 60's

Use one of your R15's as a center (and maybe the other for a single rear in a 4.1 setup) until the budget refills and you can purchase the CS1 or CS2. Then use the R15's as surrounds.

For a very modest investment you will have a top end entry level surround speaker system and the results will be a very noticeable improvement from just the R15's

Just a thought anyway. "Afrogt" made a very good point. You have to commit to a single manufacturer and speaker series for the "front 3" prior to buying any of the components. Buying a center first will "lock" you into what to buy later on for the front L & R, even if those speakers would exceed your budget and you can not take advantage of the remarkable speaker sales that pop up every so often.