You mention "time domain issue" as the possible reason for the elevated "hihats" but maybe you're conflating 2 different issues? The 8030c are designed to be nearfield speakers so that its direct sound is everything you want to hear with no consideration for reflected sound and additionally, with its smaller woofers it has a
higher crossover point at 3000 (whereas
8351B crossover is lower at 2800); taken together, these 2 factors give the 8030c the advantage in better transient accuracy in the treble where you'll most notice differences. For example from 1m away in your dead room, you will hear all of the speaker's nuances with little from room reflections which means you will be more attuned to the slightly better transient response of the smaller 8030c. My understanding of the hihat frequency characteristics is that the
body is between 300hz and 500hz but the "abrasiveness" is in the 4K range and the "sparkle" between 6K and 8K. Amir's 8351B spectral decay measurements show noticeable but narrow resonances at around 2.5K (likely at the crossover point?) - maybe this is what you're hearing? Go into GLM and see what EQ adjustments you can make to have the 8351B sound like the 8030c and then you'll know exactly what frequency is giving you trouble.
Also, a speaker's spectral decay and time domain issues may change with volume, so at what SPL are you listening to these speakers from your listening position? Try comparing at 76dB.