I've used the following over the years: Aerial Acoustics, Totem, Tannoy, Dynaudio as well as Polk Audio LSi 9's. I thought the Polks were excellent and certainly not mid-fi. Switching to Totems was a major disappointment for me in my system with all of the genres except Jazz that I listened too.
The Polk name is mid-fi but the LSi's certainly weren't. I've listened to all the usual suspects - Wilson, Revel, Focal as well as rarer brands like Krell, Reference 3a, Kudos and various Italian brands.
The LSi's were a poor mans Krell resolution - the bass wasn't as tight or clean but the airy sound with the Vifa tweeter sure was sweet. The LSi's benefitted from power. I used SimAudio and higher powered Krell, the LSi's benefited from the Krell power output.
A great fun speaker that is easy to listen too. Doesn't have the 'audiophile badge' but is certainly an audiophile speaker capable or resolving complex music with a warm tone and deep soundstage with pin point imaging. At three feet from the back wall with proper toe in (I used WASP) they really shined, a dedicated 250wpc power amp probably would have kicked things up a notch or two.