I purchased the SX50 and the 51/4 sucked. The tweeters where just ok but expected more. I sold them and bought the SX60 was still very disappointed. The midbass was better but the tweeter still sub par IMHO. I would look into something else unless you are getting a smoking deal. I will never buy that line again. Other you might also look at unless you are dead set on the SX stuff is POLK MMC6500, Pioneer 720PRS, Diamonds and cruthcfield has the MB Quart RUA216 149.99 w/free shipping. I think CDT might have some stuff in the same price range also. I only base the SX series on my personnal opinion of them I was less than happy for the price and I got them on sale for 179.99 new when I got them. I have not heard the MB Quart RUA216 though they might not be any better.
MIDBASS-less than impresive
Tweeters-some of the worst I have ever used