Actually, the speakers are the most important part of the system. Sub woofer ads a kick to movies but if you have great mains, it's not necessary, at list in the beginning. You could always add it later.
Mains and center channel should be matched and from the same company but not necessarily. Most of modern receivers offer some type of EQ.
Rear speakers handle very little information and if you need to save, that's the place.
Receiver has to handle the speakers and basically, more power the better.
If your friend can't hear differences between speakers perhaps you need to go and listen yourself.
For your budget I'd look for a used pair of ProACs or Sonus Faber. There's plenty of other great speaker. Thiel comes to mind, Infinity, Magneplanar, Martin Logan. A used pair will beat the budgisus out of Polks or Bose, but you do need to listen and make your own conclusions.
As I mentioned before, speakers adverse sound the most.
I have a pair of Pro Ac 2.5 clones if you interested.
Good luck.