Depends on what year/model MacMini that you have and which make/model receiver that you have.
If your receiver has HDMI inputs and outputs you can simply connect to the receiver via HDMI and plug then connect the monitor or TV to that. This will give you the widest range of surround options. This method applies to most all MacMinis.
If your receiver has optical or coaxial digital inputs, there are a lot of USB adapters available to connect the Mini that way unless it is an older Mini that has the multipurpose analog/optical jacks (those will be Minis with both audio in and audio out jacks). However, because of the bandwidth of the optical or coaxial interface, you will be limited to stereo PCM or compressed 5.1 surround. In this case, the receiver must have built in decoders for the compressed signals. Generally but not always, if receivers have these inputs they will support decoding of these formats (Dolby D, DTS, AAC).
If your receiver only has analog inputs, then you will generally need a USB interface that can decode into surround sound or some video/audio apps that can decode the encoded surround audio into the PCM that can be delivered to a USB based digital to analog converter. This method tends to be more complicated and can take time to set up or find the right combination of devices.
Personally, I would stick with the HDMI approach as it has the most flexible range of surround options including Dolby Atmos and up to 7.1 channel surround at 192KHz.
