Within the next couple weeks my journey to Rocket HT package #4 will be complete.

For music the 550s are wonderful. Obviously they will not be as good as the 750s but should be wonderful. I saved a bit of money by going the used/B-stock route. FYI, what I paid came out to be the following (rough figures):
RS550s - $670 for B-stock including shipping
RSC200 - $425 for B-stock including shipping
RSC150s - $250 for used. (Haven't received as of yet.)
So not bad at all for roughly $1,345. Just have to keep your eyes open.