In most cases the answer is no. The RCA outputs are wired directly to the RCA inputs. So connecting standard headphones to the RCA output connectors would in effect mean that the component providing line-level signals to the RCA input connectors would have to be able to drive those headphones, and in parallel with the input impedance of the Stax amp. Most components providing line-level outputs do not have low enough output impedances to provide reasonable results when driving most headphones directly, although there are some exceptions.
Regards,
-- Al
Regards,
-- Al