We used M&K speaker systems for years in our reference system: my favourite iteration used three S-150 front speakers, two pairs of SS-150 Tripole rears and a pair of MX-350THX subwoofers (fed by a Lexicon processor and Bryston powers: it was a bit good!).
We reviewed many other M&K systems in that period, including the smaller, sleeker S-125 speakers, the 750THX package, the compact K-series satellites and more. We've also used M&K speaker systems for at least two major public demonstrations I've been involved in (and I've been involved in a lot).
You may be aware that M&K went bankrupt in 2007, and had to close its Californian factory after 30-odd years. Ken Kreisel parted company with the brand shortly afterwards: subsequently it relocated its head office to Denmark, along with the remaining members of the original M&K design team.
Despite this setback, we've maintained good relations with the long-standing UK importer of the brand, Rob Sinden of Gecko home cinema, and in the November 2008 Ultimate Guide to Blu-ray we reviewed the company's new M-7 system, produced out of its new factory in Denmark (it got five stars, by the way). Apologies if this review doesn't appear in our Buying Guide: it certainly ought to.
The next M&K review will be appearing in the April 2010 issue of What Hi-Fi? Sound and Vision, on sale March 10th. It's the 950 series system, comprising (in this case) three LCR950 fronts, an MX350THX sub (not the normal MX250 model) plus a pair of Tripole rears. I'm afraid you'll have to wait until the issue has gone on sale to find out how it got on...