I own Europas and Quad 12L Actives. The problem is I haven't listened to my Europas in about a year and only recently got the Quads. And the Active 12's may be quite different from the passive ones, I don't know.
Rough impressions are that the Quads are more detailed and a bit more forward but probably don't image as well as the Europas and are not as open as the Europas.. I'd say the Quads, though very neutral, are a bit more "hi-fi" and a bit less refined. Funny because I would not describe the Europas as refined. Both are very good at low volume, with the nod going to the Quads.
