High end to me is a company or specific line that if treated properly will be with you for a long time. For example, many Zapco, McIntosh, etc. owners have had their amps/equipment for 15-20+ years, and still work like the day the came off the factory line. Not a whole lot of Pyramid, Legacy owners can say that.
High end also tells me that even if pushed beyond it's limits, a product should be able to maintain itself for a period of time, rather than failing immediately (extreme circumstances not included).
High end also means functionality and flexibility. Whether it be a sub (DD, W7, IDmax, etc.) that can get plenty loud, but yet it still maintains decent to excellent sound quality. And for amps, gives you the ability to fine tune your speakers/subs, and not just have a gain and bass boost knob on the side. Good amps also have the flexibility to work in various situations without problem.
High end should not only be build quality, but asthetics as well. Who wants to drop 4 digits on a product, and have it look like a steaming turd? Granted, looks aren't everything, and will usually tell you nothing about performance, but to me, if a company is willing to take the time to go over every detail in the look of the product, it gives me a better feeling about the amount of effort that went into the build quality of the product.
Other things such as customer service should be a factor as well. With any of the products you own, are you able to call the company and speak to someone knowledgable that can walk you through a situation over the phone, or offer up suggestions...or will you call, get passed around to 15 different people, and end up with someone that can offer you little more information than the retail price of the item?
And most importantly, how well does the product fit your situation or needs. ANY company IMO, has the potential to be "high-end", as long as you feel it is the absloute best product for your situation, and you know that it will be there for you for years to come.
Just my $.02