The Retarget Tab
Avastar provides an animation mapper that allows you 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