All four Macs work fine with Airplay when using Itunes. So far, only one works with iRealPro and airplay. Three of the Macs were purchased in 2013 and so are fairly recent vintage. (One of those, the Macbook Pro Retina works with IrealPro.) All of these boxes are kept up-to-date with OS changes and app upgrades.
I am going to check the firmware updates on my Klipsch speakers and will get back with you.
BTW, in the ireal app, when I click on the airplay icon, I am given an option for my airplay speakers (same as on the iPad) but also for two other speakers: Sunflower(2ch) and Sunflower(64ch). These options do NOT show up on the Macbook Pro Retina which DOES play the ireal app through the airplay speakers.