The Apollo suite of apps make it easy to integrate iOS synthesizers and sequencers into a desktop recording environment.
Sidecar on iOS can stream audio -- and Apollo Sound Injector is the Mac desktop app that can receive that audio stream. You can route the audio to the Mac built-in speakers. To redirect the audio into a DAW like Logic, Reaper, Cubase, or Live, use the free Soundflower plug-in from Cycling 74.
The streamed audio is relatively low latency, but this will depend on your WiFi network.
The apps work well with Apollo MIDI over Bluetooth, the first and fastest Bluetooth MIDI solution for iOS 7, 8, and OS X 10.7 and newer.