Speaker upgrade.
I would recommend an upgrade of the front channels. It is much better to have a good 2.1 or 3.1 system then a 5.1 system with mediocre 5.1 system.
If asthetics are also a factor on the fronts, check out in-wall or on-wall speakers. They have the RBH/EMP on-walls in the AH store for $100 each.
Also, FYI, I used some Phenoix Gold in-ceiling speakers in my distrubed audio system (kitchen, bedroom, bathroom, study, etc.). The build quality and sound is good for a budget speaker and they would work for an entry level HT. About $40/pair on Amazon.