I've used my BD player as a source throught my Rega DAC by COAX cable with good results. If I was going to buy a dedicaded CD player I would not need to connected through a external DAC ( at the same budget).
The external DAC has other abilities, like Steve have Highlight, the possibility to connect sources through is inputs ( Optical, COAX, USB)
i've my NAS connected to my Rega DAC through USB input and with greater results that BDP.
I've rip all my CD using db Poweramp program with no compretion, all i can say is that i've never heard my CD like this, i've never had a quality CD player as well...
But when i compare BDP coax, NAS USB into Rega DAC the second sounds like a High end source.