What is AS 1/2…? There is AN 1/2 and maybe AES - so what is it?
And where are your speakers connected? And what is your Cubase Master playback channel? Obviously the Cubase Master playback channel must not be the same as the Windows playback channels otherwise you are creating a feedback loop.
And the Loopback ouput channel must not be the output your speakers are connected to.
The Loopback “return”-channel is the same as the equivalent loopback “output” channel.
As said before - Don´t create a feedback loop routing in totalmix - see above.