HD650 is my go to can when I tire of the K701 sound. There are times I want a warmer, more relaxed presentation with some nicely boosted bass and deeper extension. Image and soundstage is not as layered as the K701... but its not by that much IMHO. The 650 warmth and smooth presentation more than makes up for what little it lacks in soundstage layering between the two cans. Don't let the 300 ohms scare you off. It has noticeably better/higher sensitivity than the K701.
[EDIT] Just re-read your post and you're wanting "tighter" bass than the K701. Thats one area the HD650 won't appeal to you... IMHO. Its bass has a looser, flowing, resonant syrup kind of sound that for many is a love-hate kind of thing. The K701 has some of the tightest/cleanest bass... IMHO. Bass "cleanliness" I think its one of the K701 strengths.
Come to think of it... if you don't mind EQ-ing the treble down to taste the DT880 could be an excellent choice too.
Edited by kramer5150 - 4/26/14 at 10:17am