Wait....what sports cars are you talking about? Those words are quite good at describing sports cars if you ask me. Even the no-hassle part could describe a sports car, but applies to any well designed machine.
Sports cars are all about control, but its usually talked about in terms of cornering and handling. Pure is a great way to talk about some sports cars and the more you get to the "sports" side the more pure it becomes. Most production sports cars are a long way from "pure" because they have things like carpeting, air-conditioning, stereos and cup holders. But the basics are there in a few cars like say a Corvette, or BMW M3, or Nissan GT-R just to cite a couple of examples. But a pure sports car is a race car and you can take all the crap that comes in a production car out, put in a roll cage and a carbon fiber seat, put on some new shoes (racing tires) and you have yourself a fairly pure sports car.
Now about efficient. There are a few kinds of efficient. Fuel efficient is typically not used to describe sports cars. However sports cars are quite efficient at getting power to the pavement. So in terms of power to weight the more pure a sports car is, the more efficient it is.
The cars to headphone analogy works I guess. If a Stax 009 were a $500 headphone we'd all have a pair, just like if an Aston Martin Vanquish were $25,000 cars we'd all have one too. But to tie this into the OP's document about flagship engineering, what if a top of the line sports car took 10 seconds to get to 60mph, took 300 feet to get from 60 to 0 mph, or even better to the headphone analogy, couldn't pull .5 g's on a cornering test without losing traction? These are some parameters that sports cars engineers look at when designing a car. They probably start out with some of these metrics as goals before the first prototypes are even drafted in software. And as the production cycle progresses they keep tweaking until their design goals are met and their company won't have to worry that their new bad-ass-car-of-badassitude won't get embarrassed when Car and Driver magazine takes it to the test track and puts it in a head-to-head shoot out with other competing sports cars.
That was the whole point of the headphone flagship paper. The author wanted to set some performance standards and see who's flagship headphones measured up.