As far as MyMix goes, again, I have not used it.
It appears that the basic system, connected by utilizing standard 100MBps network switches, is limited to 16 total channels on the network.
If you want more channels you can do that. The limitation of channel count is not listed in the manual. The requirements for networked channel counts above 16 are the need to use a managed switch that also has IGMP snooping. If the system has to use more than 1 switch then the switch's have to have Gigabit uplink ports.
All use also requires a dedicated network until AVB switches become available.
It also appears that the inputs to the system, and what monitor channel they appear on, are determined by the physical patch of the input and are then left up to programming each mixer to establish which 16 channels will be utilized by which mixer.
There is an 1/8" input for a local source such as a metronome.
As far as Aviom goes each system is limited to 16 channels since the mixers each only see the data connection as 16 inputs on one RJ45. You could run more than one Aviom system in order to access additional channels but, each system would only have access to 16 channels. Only one of the mixer types, the A16R, has a local input capability. It requires a rack mounted main unit and a different wiring topology than the A16II.
With either MyMix or AVIOM each system only allows a single input to the system to feed a single monitor channel. In order to achieve a sub mix you have to submix externally and feed this into the system as a single channel.
With the Roland system you can take 40 inputs and create 16 stereo (32 channel) inputs available at each mixer. You can create sub groups and send different sources to different mixers. A much more flexible system.
If you are not using Roland consoles far creating the matrix feeds (or even if you are) you utilize a connected computer to control audio assignments and store the system settings. It is not required after set up until you need to make a change.
Both the MyMix and the Roland also offer a local mic, built into each mixer, so that each user can mix a local mic into their headphones or ear buds in order to hear ambient sound without adding a mic that then takes up one of your input channels.
That's probably enough of my ramblings on this for now.
Pro Sound Advice, Inc.