Midrange Better Than Harbeth or Spendor?

I second Lindisfarne, you should definitely audition ATC.

Another option might be the classic Quad 989's but you may miss too much of the low end - so I am not sure if everyone would agree that they are better than the speakers you mentioned...although they are obviously better known for a great mid range, as is ATC.

I'm a bit surprised that no one's yet mentioned Quad.

I did suggest Quad earlier in the thread and I agree with you that a more full range design with a great mid may be preferable. Nevertheless the question was about a great mid range and therefore it makes sense to suggest Quad.

I read somewhere that the Harbeth SLH5 is slightly recessed in the 2 Khz to 4 Khz region - they are deliberately a polite sounding speaker. This may explain your impression that they are articulate without sounding harsh or edgy. The "edgy" sound you especially get from brass instruments mostly occurs around 4 Khz. If this more polite sound is what you prefer then go for the SHL5...although a jazz musician may find that this flavor lacks the proper harshness or brashiness you typically get from brass instruments (often better produced by horn speakers)...at the end of the day, who cares what others think.... as it is your choice of speaker for your tastes.

Given more clarity about your preferences in your last comment, I suggest you probably will not like ATC. I suspect you would find ATC's sound "edgy" or "harsh" in the upper mid range compared to your preferred taste. Just my two cents but I thought I would pass on this advice rather than mindlessly plug something that now appears less well suited to your taste. In fact, a three way active PMC may be a speaker worth looking into given your tastes (think ATC with a more polite or less revealing mid range and significantly more bass).

I think you are correct regarding my taste and the dip at 2-4Khz which is probably good in my small and somewhat reflective room.

If you're room is highly reflective then the Harbeth's may be the perfect "Goldilocks" speaker for you! Enjoy! Those radial drivers have a strong following and rightly so!