winyip:You got a point there but is the R45 really not up to the job? I will just hook them up for surround duty, not for front or center channel. Plus, I like its miniature size for easy mounting.
As previously mentioned, the lowest frequency that the R45s can do is 120HZ, which mens that you can't set your crossover below this and your sub is having to handle a greater range of frequencies. The R90 goes down to 85HZ which allows you to set the crossover at about 90HZ, which is better. Also, better quality surrounds will give a better quality overall sound anyway.