This is a very subjective noob review for people who aren't terribly concerned with pure signal source. I use EQ on my player. I don't compare these two headphones with the same EQ settings. I'm comparing their potential, I guess. I definitely listened to them with the EQ flat...just for kicks, but then I optimized my EQ settings the best I possibly could via Rockbox to get the most out of both of the headphones.
First impression: (just recieved the QJ's)
I've already stated that I'm pretty sure I'm not an audiophile...more of a "music enthusiast". I don't know anything about "roll-off" and "forward" and all your techy lingo'phile words. I have been looking for a good portable rig w/o being too cumbersome and spendy. I settled on the Clip+ (for now) for a source. Had the Fiio E5, but it really didn't help all that much when compared to the white noise it introduced.
I began my search with the Koss PortaPro. They were a ton better than my Vmoda Bass Freq's. The vast improvement left me wondering what else was out there beyond the $30 PortaPro...it "had" to be incredible. I got a good deal on the Miles Davis Tributes and sold them after 2 weeks. They were too revealing of poor recordings that I used to enjoy. They were also a bit harsh on my ears. I sold them and settled on the AKG Q460's. I had seriously considered the K181DJ...but went with the 460's due to their size / portability.
The first couple of seconds made me wonder if I would regret my purchase, but after about 15min they seemed to open up and really "sing to me".
What I'm noticing after my initial use is that they are a much more capable headphone than the PortaPro. They have more prominant mid range...(is this what forward mids are?)...and are much more detailed. They are louder than the PP's...I'm assuming they are lower resistance. The bass response seems more controlled, the mid's (as I stated) make themselves more known, and the treble is more detailed and crisp.
I'm sorry for the vague, non-technical verbage here, but I just don't have the experience in HiFi that you guru's seem to have.
All I know is that after about 15min of use...they sound like a whole different playing field than the PP's. They make the Koss sound thin and muffled. No amount of EQ'ing will open up the PortaPro's to compete with the QJ's. I'm very happy with them.