speaker upgrading ??

Has anyone upgraded the standard S8 speakers to some other brand of aftermarket speaker ??
Does anyone know the sizes of the speakers ? ( I have the standard non bose by the way )
I've been toying with the idea of a phatnoise but with limited funds I'd rather get the sound quality up either by changing speakers or amplification.....
Although, hopefully someone at ADI will have the RNS-E fitted for me to check out.......