If you ever came across the term ‘biodynamic’, you’ve probably heard of the famous Denon AH D-X000 series. Driven by Foster drivers, they are known for their extended low-end and dynamic bass reproduction. Unfortunately the X000 was discontinued in the end of 2012. That didn’t end the era of bio-cellulose diaphragms in headphones though. Next to new models from Fostex, E-MU and several other brands, there is still a healthy used-market for the older D2000, 5000 and 7000. While the D5k is a step up and the D7k even more expensive and rarer, the...