It also depends on what kind of music you listen to.
For example, A friend of mine has sort of similar JBL's, and they play loud and heavy music well. Not so great so classical, however, but not bad. M80's play classical music very nicely in my opinion.
I also doubt that a new amp and new speakers would fill your room better, unless you're playing stuff at a VERY loud volume. Your speakers already have built in amps for the 12 inch woofers so that takes a huge load off your receiver / amp to power the rest of the driver units in your speakers.
