According to Audio Advisor it is 16/44.1.
(see: http://www.audioadvisor.com/store/productinfo.asp?sku=POLKXRT12&InfoType=1&PageTitle=Specifications it is 16/44.1.
(see: http://www.audioadvisor.com/store/productinfo.asp?sku=POLKXRT12&InfoType=1&PageTitle=Specifications it is 16/44.1.