Thanks for the info. Now for suitability of aptX for measurements, I'm no expert, but there is
this page with a lot of info about bluetooth codecs including testing and the author found that aptX has staggering -57 dB of noise when playing a 12.4 KHz sine, which I would consider not insignificant. AptX HD decreases the noise to what seems about -70 dB. But that's just when playing a sine wave of a specific frequency designed to cause trouble for the codec. So aptX might be OK for general music listening (it was designed for that) but maybe not for testing signals. Now the difference between wired and wireless in your FR measurements is really very small, insignificant, and might be just normal measurement-to-measurement variance, but what seems to be very slightly more energy in upper treble might just be from the aptX noise (or not, I dunno). Also, the author explains that manufacturers might chose slightly different tuning for each bluetooth codec, to try to overcome its weaknesses, that might also impact bluetooth measurements.
But hey, I'm no expert, your measurements look very good and are very informative, it's just that bluetooth audio is a mess (and I base my opinions on just a few articles on the subject like the one I've linked, so again, I by far do not have all the info/knowledge). Thanks for the review