They can be called mixing consoles, mixers, mixing boards, sound boards, audio desks, or even control surfaces. I personally prefer the term "audio desk" or "console."
Take into consideration the skill level and expertise of your audio engineers.
What are all these things? Science would tell us that an audio mixing desk is a voltage summer that combines multiple audio signals to a single or multiple outputs providing a summed result of the signals. An audio desk often has circuitry that will allow the user to manipulate these signals (frequency, amplitude and phase) to provide a desired result.
Let's take a look at an entire audio system in its basics. An audio signal (voice, etc.) is converted to electricity by a microphone. This electrical signal is received by the audio desk, manipulated and combined with other audio signals. The resulting output is an electrical signal that is then sent to an amplifier where the signal's voltage is increased.
From the amplifier, the electrical signal is sent to a loudspeaker, where it is converted from electricity back into audible sound.
The audio desk is the heart of your audio system. If you don't believe me, think about the last time you had feedback or a dead microphone People at the speakers, they look at the person running the audio desk.
Not all desks are created equal, and no single desk will fit everyone's needs. Channel count, numbers of outputs, buses and signal processing capabilities, along with your budget determine almost everything about your desk needs. Most of the forums for Church Sound, for example, poke fun at certain desks as a "Swiss Army Knife" for church sound. While I agree that there are a few desks that are a very good fit for many circumstances, they all have limitations.
Are your audio engineers' volunteers? Take into consideration the skill level and expertise of your audio engineers. Some volunteers are very savvy and will grasp the latest and greatest technology, while others might only know which fader to push when the preacher needs to be louder.
Some volunteers will never grasp the concept of a complex desk, digital technology or how to operate in layers. You will need to assess the skill level of your volunteers and the amount of time they will need to learn a new technology.
Inputs and Outputs
How many inputs do you need, where do you need them? How will they get from the source to the console? What if you need to pull a feed up from another area? Are you building a new space or upgrading an existing one?
When I am spec'ing a desk for a church, I have the tech director and volunteers create a "typical" channel map. What instruments do you use, how many vocals, etc. Don't forget about computers and other playback sources like tracks, click, video playback, etc. Then list your outputs.
When listing outputs, don't forget about things like hearing impaired transmitters, lobby/nursery feeds, recording feeds, etc. There might be more than you think, and writing them down is a good way to communicate your needs to both your team and your budget.
Signal processing can be done in many ways. A basic analog desk will almost always have gain and equalization for each channel. Outboard processors are primarily used for gates, compressors and effects. This requires them to have more inputs and outputs. (Think about the chart of inputs and outputs above)
A digital audio desk will likely have some of these built in, but be aware that they also will use inputs and outputs. Sometimes the manufacturers of the digital desks will reduce the numbers of physical outputs and inputs, based on the processing being part of the desk. There is nothing wrong with this method if you are OK using the built in processing. Again, you need to determine your needs.
With every piece of technology that we integrate into our worship experiences, we need to do our research. God has called us to be good stewards of what he has entrusted with. Ask a lot of questions, talk to people who have been there and made the decision.