The StudioLive AR8 USB outputs are in Mono.
The control room outputs are Balanced Mono Outputs.
The Aux Sends outputs are Balanced Mono Outputs
Please see Section 3.1.2/Page 7 for full details.
Link:
https://pae-web.presonusmusic.com/downloads/products/pdf/StudioLiveARSeries_OwnersManual_EN_23022017.pdf