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).
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).