Windows supports and uses aptx by default on the newer builds

It depends on how much your hrtf differs from 5128 honestly. Measurements on a 43ag do show that hd600 has too much mids compared to 43ag diffuse field but on 5128 diffuse field the hd600 seems to closely match it apart from the 8khz peak that was not visible on the 43ag and the 4.5khz scoop. Meanwhile the 660s2 has some really bad dips. I already eq-ed my 600 to 660s2 and the scoop makes the neutral tonality feel off

Tonality in terms of how it sounds compared to neutral. Hd600 has a much smaller scoop than 660s2 thus making it closer to 5128 hrtf. The 660s seems to have a much worse timbre on paper too

Hd600 is objectively better though in terms of tonality

Only subbass😏

This is an easy feature Apple should implement