To move to a different sound signature from the HD650 my suggestions would be a HE560 (brighter, better sound stage, a bit more mid centric, deeper bass without the mid bass hump of the HD650) and more extended and smoother highs. My other suggestions would be to see if you can find either a Ypsilon S2 or Nhoord Red v2 build, they are like the RS series Grado that use wood cups, much more dynamic with tighter bass and cleaner highs. Look in my profile if you want to see pictures of the ones that I've built.
Thank-you @DavidA... The HE560 sounds like it needs more investigation by me. The others I haven't heard of and I'll look them up. You have quite some inventory of headphones...your experience impressions are appreciated in helping to narrow things down for me.