Yeah... Mark 2....Series 2....Second Edition....all mean the same usually..
It is also a branding thing... All the REL ST subwoofers come in a "III" version or Series 3. But some models in that ST line never has a Series 2. Calling some II would only make them appear older than the III's.
What I do find interesting is the guy selling a pair of B&W Matrix 805 "Series 2" speakers.
There is no such thing. B&W only made one version of the M805...