Probably my NAD 517 CD changer. I purchased this before I purchased any streaming media players. IN fact, it was this unit that prompted me to move to the non-compressed wav-file-streaming world. I had no issue with the 517 per se, until one day, it just got very particular about playing certain discs. I cleaned its lens, looked for obvious issues with its internals, but couldn't really find any.
It got to the point where a disc would load and play successfully maybe 55% of the time, with the remaining 45% of the time the player sitting there like it was attempting to play the disc, but never quite accomplishing said task. This was odd, because I have owned various NAD gear over the years, and never had an issue with any of it - until the 517.
That was more or less when I decided to start converting my CD library to wav files, and streaming them via my cat5 network.
I haven't looked back since, and now the 517 just sits on a shelf.