When listening to CD do you use the digital or analog output from the Blu-ray player? This makes a difference where the signal is decoded. If digital out the decoding is done in the receiver. Analog would require two hook ups, red/white (L/R) for analog use and a digital out so you can get 5.1or better surround. You should first compare the two if you haven't to see if you can gain any improvement.

To answer the DAC question, one would improve your sound quality as long as it was better than what was in the BDP or receiver.