If your A/D input is not used - then no. The pure analog circuit (PAC) is around the analog audio connectors routed to outputs (DAC) and inputs (ADC). USB audio is a different beast - living purely in the digital domain with exception of anything that would use the A/D input. If this is used (modulation source, etc) - then you would be using PAC.

Although I get the feeling like what you're asking is if USB audio - that is a direct consequence of the tone generator - will somehow benefit from PAC. And the answer here is no - since the USB signal path from tone generator to your PC is not analog. And here the signal stays in the digital domain.

However, if you are using Montage as your audio interface, then all signals benefit from the Montage's Pure Analog Circuit. You will notice even your plugins synths sound better through Montage. It simply is a very high quality audio system.

Don't forget the Montage is not only your source synth when using USB, it's your computer's audio interface.

To benefit from this analog warmth connect to the 1/4" L&R outputs of the Montage. To capture all your DAW playback through PAC connect your Mixdown recorder to the main outputs of the Montage.

It's analog!
You can never listen to digital signal.
It's like MIDI, You can never listen to MIDI (it makes no sound)!

But if audio is playing through Montage, it's using PAC.

Don't get yourself caught up in a circle... say you have really unbelievable speakers. You start thinking in a circle when you decide you want to get "the sound" of those speakers into your recording. But you're listening through those speaker... you see?!

Thank you guys, that helps a lot:)