Sounds like a standard thing. I'm not aware of your restrictions but I would actually suggest looking into some pre-made Texas Instruments ADC/DAC->USB ICs which are widely in use in existing products.
Well, my MEMS microphones are actually themselves digital (PDM) so I do not need an ADC. I will look into existing USB ICs, but I do not think I will use them as this is a learning exercise (I think I will solve PDM->USB with either a microcontroller or an FPGA).
USB is sufficient, for LPCM (assuming 16bit stereo 48kHz) requires 1.47Mbit/s whereas USB2.0 is already 480Mbit/s. HDMI generally only carries audio from a video source (PC) to a monitor, it can optionally carry audio back through ARC (Audio Return Channel), which is used by TVs that are connected to a HDMI receiver (those fancy 5.1, 7.1 amplifiers that switch HDMI), adding the ability to route TV audio back to the receiver even though the receiver generally only sends video to the TV over this cable.
Thanks a bunch :) .
So the conclusion is that HDMI supports this ARC thing, but the graphics cards do not. Well, then I will use USB.
Thanks again, Nsajko