I'd like to say that these are both excellent headphones. Would I be able to really distinguish differences between these two if they weren't next to each other? Maybe not.
I still prefer the richer sound of 400's, they go down lower and as I like bass they make each individual bass note sound more distinct. For example, on Warm Ways Fleetwood Mac the bass line on the 9500's almost bleeds together continuously instead of separate plucks of the bass strings. This doesn't happen on all recordings though. The 400's are smoother where digital high frequencies seem to soften up on less than perfect recordings. (Which is important to me since I almost exclusively listen to older recordings.) I guess another way of saying that could be that the 9500's are more revealing? Or the 400's high end is a bit more laid back. When I listened to Sting's Englishman in NY, I can hear the recording sound more cavernous, in a much bigger space with the 400's than the 9500.
The 9500's puts vocals more centered and localized in my head. They seem to have a bit of a recessed midrange...I think. You can debate me on this point.
Basically, for long term listening, I just prefer the Hifiman 400i's. If I only listened to amazingly recorded music, the Philips would be fine with me. I prefer the smoothness and less harsh sound of the 400's and the more clear bass. They also seal over the ears better. It just makes me want to listen to more music and makes me not really miss listening to my speakers. I just wish they were lighter but you can't have everything. I also would have never have bought them at $450 though.
The 9500's are fabulous at $80 (their now price on amazon) but I prefer the less, ever so slightly less boomy resonant bass of the 400's and more listenability of mediocre and bad recordings.
