For me the Q701 does well with most of the music i listen to. This is my preferred sound signature though. For a closed headphone i use an HM5, and my favorite IEM is my RE-Zero. These all 3 sound pretty similar and this is the sound i like.
Ive never heard the HD598, but i think everyone should try the Q701 at some point. Its special and hits way above the price they go for now days.