One of the best ways to determine if you system is mid fi or not is by counting the total number of buttons on your system. A lower number is more hi fi, and a higher number is more mid fi.
Although rare, some power amplifiers locate their power switches on the back panel, to discourage the user from ever turning them off. This is most certainly hi fi.
The presence of tone controls and remotes - particularly a "universal" or shared remote - pretty much guarantees that your system is mid fi, as does any subwoofer, regardless of cost.
Surround sound or multi channel audio is always mid fi.
The presence of any features designed for comfort or convenience are also always mid fi. For example, any turntable which is automatic or even semi automatic is certainly mid fi.
Recorded formats or devices which emphasize quantity, convenience or practicality, rather than effort no object quality, are always mid fi, if not low fi. MP3 therefore is always mid fi at best, and all CD and even SACD changers are mid fi.
Similarly, in wall or concealed speakers are always mid fi, regardless of their cost or alleged performance. And any component designed first and foremost to integrate into someone's living space is also clearly mid fi. So any product whose marketing materials use the word "lifestyle", or anything obviously designed to be small or lightweight is mid fi.
Everything ever made by Bang & Olufsen is mid fi, and Bose doesnt even reach mid fi status.
Samhar's makes an interesting point, but actually some Rolling Stones recordings are pretty good.
I hope this helps.