I'd be intersted in reading a responce from someone whos had both also. I was in your position not long ago and went with the HP100, listening to it right now. The way I saw it, both have good bass, both have good sound stage, both are very comfortable but I read that the beyer has dipped mids whereas the Soundmagic doesn't really. Also, the Beyer supposedly has bright highs where the Soundmagic again does not. The Soundmaagic is very even in overall response. I know the Soundmagic have very good detail but I've not read that being a particular strength in the Beyers. Both can be play with a portable device but are better with a little amp. Some dont like the look of the Soundmagics but I dont care really. They are not that bad. Obviously, you know what I chose, but what I just wrote was what made my decision.
