I own about 4 synths, and wanted to use them as 'external instruments' within Ableton. Before, I had my synths all coming in via input 1 and 2 on my audio interface, resulting in routing complications/limitations. The AudioFuse proved the perfect and, if I did my research well, most affordable solution.
I've connected my AudioFuse to my audio interface via ADAT (don't forget to remove the plastic caps on the cable tips - like I did), set the clock source on my audio interface to 'optical' and both units at the same sample rate. Then it was just a matter of selecting the extra inputs in Abletons Input Config screen and setting up the external instruments.