I am looking to buy a pair of used speakers as I have very limited budget. I found some deals on those used speakers over internet. The cobalt 815 is $100 more than S8 and cobalt 820 is $150 more than 815. So perform wise, which one is best performer for music? Price wise, which one is the best bang for the buck? I also looked into MA silver 8i which is cheaper than S8. I know the s8 is newer model. Is there big difference between 8i and s8? Another option could be PSB sivler i which is about same price as cobalt 820. Any comment is appreciated.