ok, first let me say that i LOVE my PX200's. just as much as my SR60's. listening to them right now, in fact.
however, these cans are the epitome of an aquired taste. the first time i listened to them, i thought they were crap. you really do just have to let them burn in, but after they are burned in, you may still not like them. they have an emphasized midrange which is something of a rarity in their class, and it can be taken as a blessing or a curse depending on your POV. this doesn't mean the bass is missing, but it's just not thrown at you. if you listen to the PX200's for awhile and then try to go back to anything in the portable koss line, the kosses sound unrefined and bloated. i find the PX200's to be supremely smooth with no fatigue, and they have the afore-mentioned balance of bass, midrange, and treble. the soundstage is a bit lacking, however.
as for the isolation, i find it to be acceptable. its DEFINITELY better than any portable, open can under $50, and it's a helluva lot better than my SR60's. last night, acually, i found out just how well they can isolate. i was using the computer for awhile, and when i took off the PX200's i found out that my hard drive had been roaring at an unsafe RPM for some time. it bombarded my ears when i first took em off and i was surprised at how well they block such sounds. it's even decent for a loud classroom. also, i love that they leak almost no sound. i prefer to keep my music private.
that's why i love my PX200's. and here's what i would do if i were you:
did you buy them from headroom? if so, make full use of the 30 day guarantee if you dont like them within a week of SERIOUS burning in. if you didn't get them from headroom, i'm assuming it's too late to return them since you've already opened them and have listened to em. if so, you can always sell em here for a fair price and pick up a pair of PX100's or KSC35's (the 35's DO rock, in case you haven't heard a pair).
one last thing and i'll stop rambling-- listen to a song that has strong midrange with the PX200's. the first time i listened to jonny lang's "good morning little schoolgirl" with these cans i was blown away. the bluesy electric guitar is awesome thru these cans.
here's hoping you like your PX200's