Here's a review of the M100. Nice cabinets but average drivers. Maybe good for a den or workshop. I have two pairs of Koss headphones, one I purchased in the late 70's before I could afford decent audio gear. The
Koss Technician VFR were first released in '74 and were the first headphones to have a variable frequency response that you could tailor to your tastes. The upper setting was pretty useless as it killed the bass, but the lower setting produced some really nice full bass for a headphone of that era. I think the originals had foam ear cushions that would degrade over time, but mine have an inflated vinyl cushion that works well as long as it holds air. They were almost $100 in the day so over $300 in today's money, which was a lot for a high schooler.
I got them from the same shop where I first heard the JBL L300 Summits with a
Harmon Kardon Citation 16. I would still like to get my hands on one of these amps (conservative 150W/ch) but the current C$1600 asking price is too high considering others on Ebay are only US$800. That's the original MSRP!