What is the difference between the Alpha Link MADI AX and the MADI SX units?
The difference is in the way the digital audio is connected to the unit.
On the AX version the digital audio is connected using ADAT Lightpipe. There are 3 connections each carrying 8 audio channels, this gives a total of 24 channels.
On the SX unit the digital audio is connected via 3 25-way D type connectors. The audio is available as 12 stereo AES/EBU digital I/O pairs, 4 pairs of I/O per D sub connector.