xONEx have a base policy of "two pieces" irrespective of the class of travel. Various airline you check in with may allow extra pieces depending on your elite status with the operating airline and/or class of travel. Weights can vary with each airline as well.
For AA, look here:
http://www.aa.com/i18n/travelInforma...horEvent=false
This indicates 2 pieces at 50lb ... there are fees for higher weights/pieces ...