Hi,
The 6505dn comes equiped with the duplexing unit - it prints double sided document without any issue.
However, it does not copy double sided documents to double sided, even though I follow instructions in the manual.
The link you provided was how to make double sided prints - not double sideded copies.The following link says it is not supported: http://www.support.xerox.com/support/workcentre-6505/support/enus.html?objGUID=8154
Regards,
Clive.