This announcement is out of date, and some information is deprecated. You can find up-to-date information on the Material Editor in our Help Center: https://help.sketchfab.com/hc/en-us/articles/202512446-Material-Editor
Following the new material editor features, here is a video demo of how to setup multiple UV channel from 3ds Max to Sketchfab, kindly provided by Revel:
And the related model:
Thanks to Revel, and feel free to reach out and send us your own video tips and walkthroughs you think can be useful for other users!