Definately get the speakers first. Boulder with B&W 7 series is a terrible mismatch.....not sure what your sales guy was thinking......
The salesperson knows that the boulder set-up alone isn't going to get his customer to where he wants and nobody can argue with Boulder so in all likelihood the victim will turn around and buy new speakers very soon. So he will sell both a boulder set-up and speakers instead of just speakers.
I agree with the others in that you should seek a reputable dealer that is willing to direct you to what is best for you and not him.