Getting into a mid-level system is probably easier than defining it.
Is price the determinate for categorizing a system, or is it performance? Do we call a great sounding economy system entry-level because it doesn't cost much?
I've seen small fortunes invested in loudspeakers connected to mid-level or even entry-level electronics. And I've seen the opposite. So have you.
It's terribly difficult to stuff concepts in predefined boxes—especially when they are edge cases. We might all agree a NAD receiver and a set of two-ways is entry level, but what of a pair of Sonus Fabers (in their heyday) driven by a Cambridge integrated?
I have to draw the line somewhere and wherever I do, I'll surely piss off someone. So be it.
A mid-level system has minimal compromises. More money is spent on speakers than electronics. Attention is paid to cables—both power and signal—and electronics are hand picked separates, though a few integrateds might qualify. That's about as broad and inclusive as I can get.
Now that I've stuck my big foot in my mouth and likely angered half the audience, we can move forward.
Glad I got that out of the way.