Capture stereo track 33/34 by default gets receives its input signals via USB 39/40 (Main L/R) and the recorded stereo track is played back to the mixer via USB 39/40, which 'should' be Main L/R, but USB is not an input option for Main L/R. USB is simply not available as input source. So you need to make Aux In 1, Aux In 2 or Tape In 'see' USB 39/40 as inputs. As far as I know, Compatibility Mode changes the settings to USB 33/34, so the routing has to be changed accordingly.

Compatibility Mode is not so much a 'problem' of the StudioLive mixer, but more a problem of the computer. The mixer needs a few seconds for the internal restart, but the computer seems to need a full restart, alternatively a start after Compatibility Mode was established on the mixer. You can't 'toggle' between the modes. The computer will always need a restart. The stereo track of Capture will probably show again after a correct restart.

"Compatibility Mode is not so much a 'problem' of the StudioLive mixer, but more a problem of the computer. The mixer needs a few seconds for the internal restart, but the computer seems to need a full restart, alternatively a start after Compatibility Mode was established on the mixer. You can't 'toggle' between the modes. The computer will always need a restart. The stereo track of Capture will probably show again after a correct restart."

Well Whalerstudios a restart worked!!! Thanks! There are many mysteries here not the least of which how is 39 and 40 are numbers between 1 and 34? Enquiring minds want to know;-) 4 years of engineering school and some how that topic was inexplicably overlooked. Maybe I nodded off in class? I am working hard to maintain my sense of humor on this sort of thing but it is very frustrating and time consuming at times.
I would like to continue this conversation after I have done some further testing to see if given the above I can establish the routes I want to create.

I would love to have a comprehensive "under the hood" white paper that documents this and as well as detailing the other "unsaid" aspects of the following from the Presonus "Compatibility Mode in Universal Control v4" document.

Compatibility Mode Windows Audio Routing Explained.
•
o The USB routing while in Compatibility Mode should be as follows
WDM Playback Device (To Mixer):
6x channel Device with channel indexes:
• (Tape Input Left) default routing and name: "StudioLive WDM 1"
• (Tape Input Right) default routing and name: "StudioLive WDM 2"
• (Aux In 1 L) default routing and name: "StudioLive WDM 3"
• (Aux in 1 R) default routing and name: "StudioLive WDM 4"
• (Aux In 2 L) default routing and name: "StudioLive WDM 5"
• (Aux In 2 R) default routing and name: "StudioLive WDM 6"
WDM Recording Device (To Host):
8x channel Device with channel indexes:
• (Ch 1) default routing and name: "StudioLive WDM 1"
• (Ch 2) default routing and name: "StudioLive WDM 2"
• (Ch 3) default routing and name: "StudioLive WDM 3"
• (Ch 4) default routing and name: "StudioLive WDM 4"
• (Ch 5) default routing and name: "StudioLive WDM5"
• (Ch 6) default routing and name: "StudioLive WDM6"
• (Main Left) default routing and name: "StudioLive WDM 7"
• (Main Right) default routing and name: "StudioLive WDM 8"

Digital Patching Options explained.
• In Compatibility Mode, all USB Sends and USB Returns beyond the 34x34 available channels shall be grayed out on the mixer LCD and in UC Surface. When in 34x34 USB I/O Mode, the following Digital Patching will be in place
• USB Send patch:
o Channel 1-32 = USB 1-32
o Main LR = USB 33-34USB Return patch:Channel 1-32 = USB 1-32
o *Channel 33-64 = USB 1-32 (Mirrored)
o Tape Input/Digital Return = 33-34*64S
• USB Return patch:
o Channel 1-32 = USB 1-32
o *Channel 33-64 = USB 1-32 (Mirrored)
o Tape Input/Digital Return = 33-34
• *64S
o For any other channel, patching should default to USB 1

There seem to be a few possible "you can't get there from here" aspects to the above.

Thanks Again!!!
Bill