Airfoil

It's easy to use, it adds an system-wide eq to your system, it let's you control the volume of devices that otherwise couldn't be. Such as digital outputs that do not negotiate their connection (TOSLINK).

Macs have built-in audio routing, they've had it for ages now, but it's been only out and only one output unless you set them up in advance in Audio MIDI Setup, which will make you lose volume control BTW. With Airfoil you can enable and disable from everything connected and detected on the network on the fly. Airfoil Satellite (included with Airfoil) allows you to receive from AirPlay sources which can then be repeated from Airfoil, or the system and let Airfoil handle one thing or the other, there's a lot of combinations available with only these two apps.

Airfoil additionally lets you correct sync problems whereas with AirPlay alone you can at best enable-disable devices and hope for the best. It's not exactly easy and it's the only negative I can think about it, because you can only correct it directly in the transmitting Mac, which means you have to ARD/VNC into it, as it's likely to be a fixed Mac away from the out-of-sync devices. It should've built it in the client apps. Probably it is already, that's the one other issue I have, now that I think of it: they stopped supporting pre-Catalina Macs, the ones you don't own anymore.

Then again, other apps like this would break every year too, the ones that dared allowing you to have some control of your system.

Airfoil's devs for what it's worth, will personally email you when you have a question, despite of their schedules, they'll listen and might actually implement your feedback which is always voluntary (no telemetry). You get discounted upgrades and upgrades to bundles. I can't think no higher for customer support/satisfaction.

As for new users; the app isn't free, it is a trial, which means a short demo to try it out. It's not a subscription, nor ad-supported, nor user-data supported because it's paid. Costs/devs have to be paid, and then again if you want the next version which you are not obligated to get. That's how it was done before devs were forced to compete for free for visibility in the app stores and resort to data mining in then subscriptions. Even if you use it just once, which I promise you, you will not, it's not expensive and if you live post-Catalina, I'm sure you spend much more renting your Mac on a month or two you just don't realize it, this app you get to keep, you don't need an account on any remote server to reactivate it.

Intermittent Audio Pitch Distortion. In an effort to route Apple Music into my high end stereo equipment I tried using Airfoil on my Mac and installed the matching Airfoil Satellite app on an old iPhone, using the headphone jack output into my amplifier. When it worked, it was a reasonable solution. Unfortunately, with no warning it would periodically shift the pitch of the music being played- think slide whistle. It was intolerable. FWIW when the Mac’s disk or network were really exercised it stuttered also. None of these symptoms occurred when routing the sound output through the MacBookPro, so it’s clearly an Airfoil issue. Previously used an Android app called Airtight that worked well emulating an AirPlay receiver until upgrades at Apple caused it to start stuttering. Really don’t want to spend $100 for an AppleTV to pipe sound, but I’m without another good solution at this point.

Tech specs used: mid 2014 rMBPro running macOS 10.11.6 I installed v5.6.4 of Airfoil, and then installed the current Airfoil Satellite App on an old iPhone 5 running iOS 10.3 (latest available from Apple).