This was my experience trying the 6xx coming from an Arya Stealth. At first, I couldn't stand listening to them due to their small soundstage, but after a couple of days I got used to it and was able to appreciate them for what they were. Eventually, I couldn't throw the Aryas back on; it turned out I much preferred the Sennheiser tonality over the Arya's. For my music preferences (music with vocals essentially), the 6xx was a much better match.

I did prefer listening to instrumental music through the Hifimans, but I realized I only listened to those genres as much as I did because I had the them. Once I got the 6xx, instrumentals became again a small portion of my listening time, and thus I could no longer justify keeping the Arya and I returned them.