I am glad to hear that. Most products that have both SD and USB capability do allow simultaneous recording. However, it isn’t obvious to me how this is managed because, as far as I can see, everywhere there is a setting for USB, it applies to both USB and SD.
I have been able to record multi-track to SD card. I then change all my channels to make the source USB/SD. And from there I can load one of the recordings from SD card and play it through the mixer, mixing each channel as if music was coming in over the XLR cables. No problem there. What I don’t understand is, if I am also using a DAW, how do I tell the mixer to get the streams from the USB interface (i.e. the DAW) instead of the SD card?