That, my fellow GM, is really the crux of what running this crazy game is all about. I don't know the answer other than your players must understand they need to be patient with you and each other.
Shadowrun more than any other RPG I've encountered excels at segregating the PCs by virtue of its myriad juxtaposed-yet-not-always-easy to interact settings: How long can you try to make justice of the astral plane for the magician player before everyone else gets glassy-eyed or their small-talk starts to get distracting? How much can you detail the Matrix in interpreting the myriad account-creation and/or hacking tests so as to engage the hacker before the rest of the group buggers off for a smoke? Sure, in game time it goes zippy fast since they get 3 initiative passes but that just means your real-life players have to wait longer. A "balanced party" in Shadowrun certainly demands more extra care to run than a "balanced party" in D&D/Pathfinder, in my experience.
Yes, you can have layered encounters where the magician is tangling with the astral security
while the grunts are neutralizing the critters
while the techy is disabling the blast doors
while the hacker is editing the footage but man, you're not getting more than 3 combat rounds done that session. At least until the rules get familiar. Maybe hold off on the hundreds of pages of extra stuff from the supplements until things gel.
The settings are rich enough that you probably
could have a party of just hackers or just adepts or just riggers etc. But all of those settings simultaneously is a big part of what makes Shadowrun tick conceptually. It's also a nightmare to run. I'm lucky in that my players have all run games before and are already hooked into the setting so they're generally more than willing to let everyone have their turns.
Good luck

and thanks to anyone that can post anything actually helpful rather than just commiseration like I did

; I'm also interested in other strategies.