Just chiming in with my experience, I'm running an AR8 USB that is more often than not plugged into an Ubuntu workstation. It works out of the box as one monolithic device with 8 embedded channels, but if you want to use it as an audio interface for applications that might not necessarily be JACK aware in some scenarios (example use case: audio interface for OBS, Discord, Zoom, etc.), then there's a really easy tweak to break it out into separate devices.
In Terminal:
sudo gedit /etc/pulse/default.pa
That will open a text editor window, where you should append the following into the end of the config file:
# Remap Presonus inputs separately
load-module module-remap-source source_name=ar8-chan-1 source_properties=device.description=StudioLive_AR8_Channel_1 master=alsa_input.usb-PreSonus_StudioLive_AR8-00.multichannel-input remix=no channels=1 master_channel_map=front-left channel_map=mono
load-module module-remap-source source_name=ar8-chan-2 source_properties=device.description="StudioLive_AR8_Channel_2" master=alsa_input.usb-PreSonus_StudioLive_AR8-00.multichannel-input remix=no channels=1 master_channel_map=front-right channel_map=mono
load-module module-remap-source source_name=ar8-chan-3-4 source_properties=device.description=StudioLive_AR8_Channels_3-4 master=alsa_input.usb-PreSonus_StudioLive_AR8-00.multichannel-input remix=no channels=2 master_channel_map=rear-left,rear-right channel_map=left,right
load-module module-remap-source source_name=ar8-chan-5-6 source_properties=device.description=StudioLive_AR8_Channels_5-6 master=alsa_input.usb-PreSonus_StudioLive_AR8-00.multichannel-input remix=no channels=2 master_channel_map=front-center,lfe channel_map=left,right
load-module module-remap-source source_name=ar8-stereo-mix source_properties=device.description=StudioLive_AR8_Stereo_Mix master=alsa_input.usb-PreSonus_StudioLive_AR8-00.multichannel-input remix=no channels=2 master_channel_map=side-left,side-right channel_map=left,right
# Remap Presonus outputs separately
load-module module-remap-sink sink_name=ar8-usb-1-2 sink_properties="device.description='StudioLive AR8 USB 1/2'" master=alsa_output.usb-PreSonus_StudioLive_AR8-00.analog-surround-40 remix=no channels=2 master_channel_map=front-left,front-right channel_map=left,right
load-module module-remap-sink sink_name=ar8-usb-3-4 sink_properties="device.description='StudioLive AR8 USB 3/4'" master=alsa_output.usb-PreSonus_StudioLive_AR8-00.analog-surround-40 remix=no channels=2 master_channel_map=rear-left,rear-right channel_map=left,right
That will create one audio device per channel strip on the board, and two audio devices for the USB 1/2 and 3/4 channels. This could theoretically be extended out to the AR12 and AR16 if somebody wanted to take the time to find the corresponding channel mappings here.