av.stage is actually the current's SWF stage, you can access the stage object of a SWF with the property stage of any DisplayObject belonging to this SWF.
If i'm not misleading, this should work (if your SWF asset contains any element):
av.getChildAt(0).stage.quality = 'whatever';
Unfortuneatly, this does not fix it, I've also tried calling
mc.stage.quality = "low"
and that has the same effect.
Any Other ideas?
Sorry i talked to fast...
In fact I think there is only one instance of the Stage object in a running player. So the only way to do this would be to rasterize your Sprite and store it in a BitmapData object, changing the quality of the stage juste before rasterization and then restoring back after. There is something in the doc that talk about this kind of thing: http://help.adobe.com/en_US/as3/mobile/WS4bebcd66a74275c36c11f3d612431904db9-7ffb.html
Hope this is helpful...