SAC is a Specialized Product
The Software Audio Console is a purpose built software. The reason for its development was and is to provide a means to mix live sound 'in the box'. The 'dream' of the developer, in my opinion, was to provide a way to mix virtual live sound that gave the sound engineer all of the tools needed to do a good job in the live venue similar to the advantages of the Digital Audio Workstation in the studio. The software includes the features of state of the art hardware digital consoles plus a few advantages gained by working in the virtual realm. I don't believe that it was ever intended to replace the big hardware. I believe that it was intended to offer an alternative solution to the task of mixing live sound with some advantages offered in the virtual world.
In order to make SAC a reality speed is of critical importance, both in the signal path through the computer and navigation around the console. The concept of SAC was formed and the initial coding was done in the mid 90s but it was the 2000s before computer hardware was up to the task. When generally available computer hardware was able to provide the needed performance the software was released. The program is written in assembly language. According to the WikipediA article on assembly language programming there are advantages for real time operations and interfacing with hardware. The article also mentions that when timing is critical assembly language programming is a good choice.
The same type of audio hardware that is utilized by a SAC rig is used for most computer audio interfaces. More specifically the necessary multi-channel input and output devices are used by DAWs in the recording studio industry. Because of the market penetration of the DAW software there are many good options for that hardware, both in the professional sound cards internal to the computer and the AD/DA converters external to the computer. As far as sound cards there are also USB and Firewire options with internal converters for use external to the computer, but channel count is usually limited with these options. There are also some other more professional options available now and more to come in the relatively near future no doubt.
For production of live sound speed is important for the engineer. With analog hardware there is a physical knob or switch for each function. Digital hardware boards can easily offer many functions onboard that required external auxiliary equipment in the analog world. Because the boards are feature rich surface real estate can be a problem. Some controls are made to be common and the channel they effect must be selected. In some cases there is not even a physical fader for each input channel so bank switching or paging must be employed. This is also the case with SAC and because of the limitations of input devices some additional features have been developed to allow virtual live sound mixing, for the most part, with only a mouse and keyboard.
With a hardware console control surface area can be a problem. With a SAC rig the monitor size and resolution are the limiting factors as to how much information can be displayed. However, on a screen the density can be higher because there is no need to allow room for fingers to touch the controls. There are features within the software to allow the onscreen view to be changed to fit the situation. Other features allow multiple faders to be moved as one. Other features allow parameters to be adjusted as one. With SAC there are several ways to accomplish any task. The choice of the particular method to do something can vary with the situation. The features of the software do all the engineer to handle nearly any requirement in the box with ease.
Disclaimer: While I have used a SAC rig for several years and analog consoles for years before that my experience with hardware digital consoles is very limited. Any inaccuracies in my depiction of hardware digital consoles is purely from my ignorance and not intended to mislead in any way.