I was hoping someone could provide their opinion on a speaker decision. I currently have the JBL scs136 speaker system. I want to upgrade the center channel. I am on a budget and am trying to decide between two speakers. I have found an open box Polk CSi30 for $115 at CC. I am alos considering the JBL N-center for around the same price with shipping. What is your opinion on which to buy and how much of a difference do you think haveing a polk center with JBLs would there be in sound. Thanks for any opinion you have.