The Retarget Tab
Avastar provides an animation mapper that allows to map foreign armatures to Avastar rigs as long as the armatures are compatible. By default Avastar expects rigs with a T-Restpose. However, the condition for a successful import is actually:
The imported animation must use the same restpose as the Avastar character
So, if you convert your Avastar rig to a compatible restpose, then you can import and map any animation