Don't buy him a knockoff. He wants Beatz because they're Beatz. It's a trend.
Also, don't buy him another brand of high end headphones. He doesn't want high end headphones, he wants Beatz.
You could also teach him not to be a dumbass who buys things solely based on trend. Getting Beats due to popularity at this point is laughable. Shit, I'd make fun of him, be like "yeah you're about 3 years too late to wear Beats for any cool factor".
Or the suggestion of making him work to earn the damn things himself. He wants trendy crap, he's gotta earn it.
Wait, wait, Beats are made by Monster? I noticed there's a chip in them with the Monster label. And they're $300?! Tell him to get some proper high end cans if he's going to spend that much.
Also, do what my dad did and tell him to save up and buy them himself if he wants them so bad.
I just looked it up, actually they broke off from Monster and are now they're own company. Monster actually made some good quality headphones, although I don't know if any of the Beats ones can claim that. The Turbines were pretty good (especially since you could get the ones with like $300+ MSRP for like $150).
It isn't the sound, it is about dumb 6th graders and brand. I have athm50s that he even acknowledges sound "awesome" but they are not beatz.
When I say knock offs I am referring to the counterfeit s that are all online that look really close
I believe some actually measured better than the official ones, but it'll be a total crapshoot and don't be surprised to get something really bad. Of course I believe some of the actual Beats have build quality issues (I recall that I think the hinges on one of them were prone to failing).
You could be a cool dad and buy some knockoffs and transplant some better drivers in. Do some little thing to add some personalization and then let him gloat that he got some extra special edition ones that both sound better and are custom for him. Maybe get them sent to Colorware or one of those places and give it a custom paint job to stand out.