Music making and audio processing has been growing and changing on iOS. The first app connections were with Audiobus, and then Inter-App Audio became available. The current standard is AUv3. There are many legacy apps and audio hosts, however, that have not updated.
Wireless Audio AUv3 gives you an easy way to send audio from one iOS device to another using a low-latency WiFi connection; you can also connect audio unit hosts together -- either on a single device, or between devices using WiFi. There are no cables and boxes to buy (and to lose, or forget to take with you). Install the Transmit AUv3 onto an audio track of one host, the Receive AUv3 on the input slot of the audio track of another host, tap `connect, and audio will be sent from one place to another with surprisingly low latency.
The receiver can adjust buffering to maximize audio quality while minimizing latency. While your best results will be with a fast WiFi router and little cross-traffic on the network, you can still get a good connection even in noisy environments.
Most modern DAWs support latency compensation, with the Receiver AUv3 reports -- this allows you to get precise synchronization of your recordings.