Bela does not currently have a streamlined workflow for streaming audio inputs to a host computer. There are ways to do it that send the data over via the USB connection as network packets and not as audio frames (e.g.: https://github.com/giuliomoro/bela-to-matlab/. This could work for some applications, although the latency may become very large (100ms or more) when you want to send high-bandwidth data such as your case.
Getting 12 channels of audio-quality input is also borderline impossible with current Bela hardware. We have the Bela Mini + Multichannel Audio expander that has 8x channels at 44.1kHz and 8x additional channels at 22.05kHz, although the quality of these lower sampling-rate one is significantly lower than regular audio channels.
Honestly, if you are looking for a plug-and-play way of streaming 12 audio channels to a computer for real-tiem usage without any embedded processing involved (now or in the future), you are better off getting a soundcard.