Not a lawyer by any means, but I am an engineer with some background in patent law.
Beats will lose this one, and badly, unless this is a suit regarding trade dress and that customers are confused. I can't imagine any patents regarding *functional* design that Yamaha could have violated, and any they may possess will likely be thrown out for failing non-obviousness. With trade dress, they might have a point, but that's notoriously hard to prove, as the Apple v Samsung case proved (where Samsung literally copied even the packaging and wall warts), and the second point, misleading customers, is even harder to prove without an extensive customer survey and guest paid consultant experts.
What Beats is really trying to do is get Yamaha to settle. Neither actually wants this to go into trial, because even if Yamaha wins, it'll have to pay its lawyers, as unfortunately, unlike many other countries, there aren't automatic implicit "loser pays" rules (and by loser pays, I mean plaintiff pays). Fortunately, there are some lawmakers in Congress pushing for patent law reform, and we might see a sort of plaintiff pays rule come into effect, which in theory should substantialize reduce the amount of trolling. As it is, however, no one wins but the lawyers making a payday if this goes to trial, so expect a settlement.