You may be better off asking on the Bethesda forums (forums.bethsoft.com) - there's a whole forum dedicated to the Creation Kit and modding. There's no native .nif exporter for Max so you have to use 3rd party tools to get anything from Max into the Creation Kit. Whether new animated characters are possible or not I don't know.
Max 2016 (SP1/EXT1)
Win7Pro x64 (SP1). i5-3570K @ 4.4GHz, 8Gb Ram, DX11.
nVidia GTX760 (2GB) (Driver 430.86).