Alright, I bought the Audigy 2 ZS platinum for $175 (shipping included) with a $100 mail-in-rebate. I recently found the Audigy 4 going for $43 with $5 MIR (shipping included). What are the major differences between the two? And, do you think I should return the Audigy 2 ZS PL. and get the Audigy 4 to save some money?