Thinking backwards I would give up my center channel first then surrounds and good luck taking my sub or fronts away from me. It just couldn't happen.
My feelings are you go as big as you desire on the mains because your mains are everything. Then invest in a great sub. A sub may only cover a tiny piece of the frequency range but it adds more to a system than almost anything else. I am continually blown away at how much my Hsu sub adds to music and movies. It is FAR more an essencial piece than any surround sound element could ever be.
