Patience, patience. Not everyone is around all the time, so it might take a few hours to get a response or two.

You seem to be satisfied with your system right now, other than the sub which you are planning to upgrade anyway. You don't necessarily need to upgrade anything else. If you can't resist scratching the upgrade itch, then your room size has a lot to do with what you should try next. How big is the room your speakers are in?