The USB output can never contain the FX from the mixer, you need to send the FX RET signal to your DAW.
Launch Studio One
Create a new song using the template for your mixer.
StudioLive 32 Series III = StudioLive 32 Session
StudioLive 24 Series III = StudioLive 24 Session
StudioLive 16 Series III = StudioLive 16 Session
The reason for using these templates is that all inputs/outputs are mapped and it makes this process easier.
Once open you should see metering on Ch1 in Studio One, this is the dry signal from the mixer. If you wish to have the Fat Channel settings on this you will need to change the Digital Send Option for Ch1 to Post.
Select Ch1, press the “Cog” Icon and make the change on the screen. Please see Section 5.2.1 and point 7 for details on this. Link: https://pae-web.presonusmusic.com/downloads/products/pdf/StudioLive_Series_III_OwnersManual_EN_14052018.pdf
You will note that each channel’s output is set to return back to the Mix, if you wish to send Ch1’s recorded audio you will need to change output to “2 Track L/R” and this will then send the audio out into the Tape Input on the mixer as per the article linked above.
On the mixer press Mix15
Then set the main fader to unity
On this channel you are just going to higher up the fader called FX RET A which is the return for FX A
Then note that on Mix 15 you have metering, this is just the FX (wet signal) of the FX and not the dry signal
Now we need to do some digital patching.
On the mixer go to Home > Audio Routing > Digital Patching > USB Sends > Then set USB 2 output to be Mix 15
On Studio One you will now see a signal on Ch2 which is USB 2 which in turn is Mix 15’s audio signal which contains the FX A sound and not the dry sound. You can now record the on board FX.
The above is just a example of how to set this up. You can setup and Mix you wish, link two mixes for stereo and use and channel in Studio One for the best work flow that works for you.