I'm a H590 owner and will get right to my points.
You have the bones for an awesome system but have to get a decent streamer. Right now you're driving a Shelby Mustang in first gear only (there are 5 more upshifts). To realize the full potential of the KEFs I would look for a streamer $2k and up.
I would forget USB out of a mac mini into the Hegel, the jitter will compromise what the rest of the system can do.
Hardwiring (no wifi) will be superior to keep the noise down. I even went to the length to remove two network switches that were splitting signals and when to a home run from the router directly to my streamer and got a noticeable improvement which was a very inexpensive upgrade. Many of the dedicated high end streamers don't even have a wifi option and they do it for a reason.
I personally run Isoacoustic feet on my speakers and subs. I have a floating hardwood floor and the aftermarket feet are worth the investment esp. for the subs. If you have hard floors give them a try. Not sure what the result would be over carpeted flooring. Maybe another user could advise us?
Bottom line is you have a fantastic system and a $2K+ investment in a really good streamer IMO will bump up your SQ by 20% or maybe more. Airplay is your weak link.
If you want to try the shallow end of the pool--first try Tidal connect with a free trial. Tidal connect is HQ audio, similar but different to the high rez Apple music option. Connect your H590 directly to your network via the Lan port and once your Hegel is on your personal network you can bypass airplay and play Tidal connect directly from your network. This will be a OMG moment where the soundstage will get wider, deeper and the bass will be MUCH cleaner. Good luck and cheers.
