I have a Yamaha RX-V473 receiver and a pair of Polk RTi8's. I know I want to get both a sub and a center, but I'm just wondering what people think would be better to get before the other. If it helps any, as far as subs go I'm looking at either Polk PSW505 $190 at Newegg or a mfr refurb Polk DSW pro 440WI for $243. The center I'm considering is mfr refurb CSi5 for $225. Thanks a lot!