Anyone feel free to correct my interpretation, but I think mid-fi is those brands which used to be above the big box stores, but were not top shelf components.
A few years back one might have considered Rotel, Adcom, Vincent, some Marantz, low end Paradigm, low end B&W, low end PSB, stuff like that.
Nicer than what Best Buy sells, but not the most expensive stuff at a full fledged high end shop.
The lines are getting quite smeared though by some of the aforementioned companies coming out with spectacular sounding products at previously unattainable prices, and some of the higher end companies bringing lower cost products to the big box stores.
