Yamaha or Infinity for Surrounds/Backs?

[Jmobie]

Our family just purchased the Yamaha RX-V663 yesterday to begin re-building our HT for hi-def. We currently have two Yamaha towers, a Yamaha sub, and an Infinity center and two Infinity bookshelf rears. We'd like to add two more surround speakers either as the surround pair or surround back. I guess the budget would be $300 at most for both. A few questions..

Which brand is better? Infinity or Yamaha?
Are these Yamaha speakers good?
How about these Infinity speakers?