Welcome to the forum. The Sundaras should be a good upgrade that shares the same sound signature. If you found the SHP9500s too bright, I’d suggest considering the Sennheiser HD6XX. I personally opted for the HD6XX over the Sundara.
Another possible option that I haven’t heard yet is the ibasso SR2. See some impressions here, mostly positive: iBasso SR2 - Official Thread.
Note that these upgrades will likely call for a slight upgrade in amplification to reveal themselves to something like the Schiit Magni 3+ or Asgard 3 (and a DAC such as the Modi 3+ or Modius).
Good luck.