Just sell him the Monoprice stuff at half the price of the Magnolia stuff and call it a day. Your wallet will be fatter and happier.
I can see myself getting into some trouble doing that

As great as your Kefs look, that's still way too much. You're talking about $300 per speaker, and that Best Buy link is to a
pair.
But I agree with you that you need to hear them in person. Unfortunately it's not possible with some of these, and I'm not going to let my clients get ripped off by Best Buy if their speakers are that grossly overpriced.
I have some Kef in wall speakers in my bath room. It;s worth remembering that some kind of sub will be needed as building speakers into the wall just suck the bass out of them. In my experience anyway.
We'll definitely add a sub. He wasn't so sure he wanted one at first, but I was insisting on that part.