Yeah, I'm not sure you are dealing with a jerk or anything. While the person is definitely not trained on Yammie equipment so it obviously clueless, he may very well be doing his job by denying the cross-over between Best Buy merchanside and Magnolia merchandise.
Not just contracturally, but if there were to be some problem with the hook ups, I believe mini-Mag keeps their accounting completely separate from BB, so who is going to eat the cost if there is an issue? The mini-Mag guy isn't trained to hook it up properly (yeah, right) and the BB guy isn't trained to work with those 'nice' speakers correctly (yeah right). It's a no-win situation really.
Depending no your location, you should be able to find a real audio store that carries Yamaha and be able to actually demo Yamaha gear in person. Likewise, getting stuff in your home to demo in real life is a great way to do things. Using your own wires, a couple of different speakers, and a couple different receivers. Find what you like best, then keep it - return the rest.