Currently, there are three ATSC tuner types that are supported in the MIO/MIO+ receivers. The supported tuners are Hauppauge 850, 950Q, and 955Q. Drivers for these tuners can be downloaded from the Plugin feeds. TNAP images for North America will have these drivers installed by default when possible.
Every combination that contains two of the three supported ATSC tuners have worked for me in the MIO receivers. The combinations I have tried are: (850, 850), (850,950Q), (850,955Q), (950,955Q). I am fairly certain that any combination of two supported ATSC tuners will work in the MIO receivers, but I have not tried all possible combinations.

It may also be possible to use more than two ATSC tuners in the MIO receivers. For the main purpose of this thread, we will only discuss using no more than two ATSC tuners. Using two or more ATSC tuners allows extra benefits in recording programs, streaming programs to other devices, and using a split antenna system where two terrestrial antennas are pointed in different directions.

Two benefits of recording with two ATSC tuners are (1) being able to record channels on two different muxes or frequencies, and (2) being able to record channels from a single mux or frequency while being able to watch any other channel that is available for your antenna system.

It should also be noted that ATSC support for the Hauppauge 850 and 950Q usb devices stopped for a brief period of time, probably only in images with a kernel of 5.2 and 5.3 due to driver issues. Support for the Hauppauge 850 and 950Q usb devices was restored in images for the MIO line of receivers using kernel 5.4.0 and 5.4.1. Most of the current images are using kernel 5.4.1, which supports all three ATSC devices.