Hello Antonio,
These blocks do not currently support multichannel audio (above 2 audio channels), and editing these library blocks is not a supported workflow.
However, if you really wanted to you can edit these blocks by breaking the library links and editing the S-functions to handle more audio channels. In order to do this you can first follow the steps below:
1. Right-click the block (either 'ALSA Audio Capture' or 'ALSA Audio Playback') and navigate to Library Link > Disable Link.
2. Right-click again and navigate to Library Link > Break Link.
3. Once the link is broken, right-click the block again and navigate to Mask > Look Under Mask. Once the Block Parameters dialog window appears, click the 'Edit' button to open the S-function associated with this block.
At this point, you will need to edit the S-function's code appropriately in order to allow it to handle multichannel audio. Please note that this may be difficult or time-consuming to implement and it is again an unsupported and not recommended workflow. You can read more about S-functions in the documentation overview below:
https://www.mathworks.com/help/rtw/s-functions.html?s_tid=srchtitle
