'Linking' probably refers to linking stereo inputs on the Earmix.

Note that linking stereo inputs on the Earmix will prevent panning: You can change the stereo width but a keyboard player to your left will be dead center in your ear mix. Leaving the channels unlinked gives full freedom regarding width and panning and then you can group pairs for one knob level control.

The input "source" of kick, snare and drum kit can be either analog or digital, so if you send signals from your DAW via USB to 32R inputs 1-4, they are automatically available in the AVB network as inputs and outputs. But don't ask me how to use virtual instruments. I would rather take a drum machine...

And "linking", yes and no. Yes for the "functional" subgroup C+D as "carrier" for general sound related events and "No" as very good option for L/R instrument channels. The organ and piano sounds will be heard left and right when linked, which I think is kind of normal and suitable for most musical environments. But you can also give them a "stage position" in the scenaro and for that the grouping of channels is perfect and probably always better than linking. It's great that the EarMix 16M has this option!

"Linked" for subgroups means that subgroup A+B or C+D are linked and panned stereo, because they "carry" stereo signals like effects (especially reverbs) and room sound (ambience microphones), also tracks are mostly stereo. FX sends are mono, FX returns are always stereo. In-ear monitoring needs a lot of stereo sound events to sound stimulating.

EarMix personal mixers are perfect for studio work. As they can be daisy-chained, it doesn't even need an expensive SW5E AVB Switch. But how do you get all the tracks and channels and buses and this and that down to 16 normal EarMix input channels? Here is an episode of three short articles, describing how to use EarMixers in studio work and how easy a set-up can be when you use default AVB settings.

The first screenshot shows the probably most important page of UC Surface. Studio work means that it is needed to switch input sources quite often. This is possible per channel (-> settings), but it also also can be done on this page. It takes about 12,7 seconds or so to change the input source of 32 channels from Analog to USB... (or vice versa) Just select the "Source Type" and then click on the channels to which you want to assign this Source Type.

A very helpful feature, saving a lot of time and you always SEE the input source of any input and output (yes, output can also have different inputs).

Screenshot 2 shows a flex mix layout with EarMixers in mind and a normal band set-up with several singers. The first channel bank (1-8) of the EarMixers would be filled with stereo mixes, channels 9-12 would see single mixes, channels 13+14 would be used for "Miscellaneous" and channels 15+16 would carry anything related to "Studio" like Talkback, rough mixes, click... As you can see in the "Routing" tab, AVB outputs of aux "Drums" are set to 41 (left) and 42 (right). This is default routing of the Series III mixers. You don't need to assign anything. It's already there, so use it!

Accordingly Aux 15+16 are assigned to AVB Sends 55+56 and "Voc 1" (Aux 9) is assigned to AVB Send 49. Aux 1-8 use AVB 41-48 and Aux 9-16 use AVB 49-56. AVB 59-64 is "free" (not used by default settings).

Linked flex mixes do NOT pan signals, linked input channels are set to "center". You have to set panning individually PER CHANNEL.

Screenshot 3 shows how the EarMixers connect and all you have to do is to select the correct AVB Sends, which is 41-48 for "1-8 Source" and 49-56 for "9-16 Source" aka EarMix input channels 1-8 and 9-16. Then hit "Apply" or "Apply All" if there are several EarMixers connected. You can daisy-chain several EarMixers by CAT5e/CAT6/CAT6A cables. You don't necessarily need a SW5E AVB Switch.

The input channels of all connected EarMixers will now have the Drums stereo mix on channels 1+2 (link needed), Bass stereo mix on channels 3+4, Keys stereo mix on channels 5+6 ... and the Studio stereo mix on channels 15+16.