Speakers known for great midrange.

Trick question.  The answer isn't a stand mount and it takes more than the INT25 to drive the planars that  set the standard.  :) 

30.2's, AudioNote Hemp, Spendor 1/2s, Have enjoyed them. Not syrupy though.

I think what you are looking for is a resonant cabinet design. I have a pair 

of old Spendors with my INT25. 

Dynaudio Special 40 and the Pass a nice match. Not syrupy but a huge fun factor. 

Harbeth is a good match with PASS, but it will be a bit "laid-back", not in a bad way, it will work very well with acoustic, vocal, jazz, classical, however if you're into AC/DC or Metal music types, it will not be a good match. My opinion as I own the Harbeth 30.2s and almost went with a PASS with them.

@mr_m  - but then you'd really need four 901's, one in each corner and then play Dark Side of the Moon at full volume with a 200 watt 4-channel Pioneer receiver from 1982....not that I ever did that of course.....

I love my Harbeths and also have KEF Ref 1 which have very good midrange and incredible imaging.

A friend completely re-did his system recently and has a pair of the Joseph Audio Pulsar2 Graphene speakers with a Pass Int-60.  I'm a little jealous of his system.  Not only does it have great midrange, but spectacular imaging and the combination is incredibly "fast".  When a note stops, it stops.  When there's a space between notes, it's black.  Pitch black.  Black hole black.  Hard to describe, but once you hear it, you can't un-hear it.