Settings for 3.1.2 audio?

I'm getting a new soundbar today in the mail, the soundbar in question is the Samsung HW-Q600A 3.1.2 Dolby Atmos soundbar. I will eventually upgrade it with rear speakers for 5.1 audio, but in the meantime I'm wondering what settings should I use? In the codec tweak tool, there is only stereo, 2.1, 4.0, 4.1, 5.1, 6.1, 7.1 and "same as input" options. Thanks!

EDIT: To clarify, I'm using the latest version of K-Lite with 64-bit MPC-HC on Windows 11.

Windows itself also does audio mixing. So you can select "same as input" and customize speaker settings in Windows Sound.

But it seems it is a 5.1 device by default. 3 front, 1 bass, 2 side.