I have some and they are very good. I would have gone for the Arya or possibly one of the electrostatic, but I was concerned with longevity. Heard a lot of bad stories about hifiman and that the electrostatics are rather delicate.
I have never heard of anyone having those sort of issues with a sennheiser.
Just run it on an equalizer if you have problems with the 5khz peak.
I don't.
I bought a hifiman he400se and after deciding I wanted more I figured doing it in stages was just going to cost more money in the long run and endgamed with a HD800s.
Unless I win the lottery or something I won't be upgrading any further.
I do also have a pair of blessing 2's but that is for listening in bed where headphones are impractical.