The HK 525 uses Cirrus Logic 192/24 DAC's. YOu can get that info at harmanaudio.com.
As far as the best to use, I would hook it up both ways with good quality cables. You can toggle between the analog and digital input selection modes on the receiver (I am sure you can do that witht the 525) and see which sounds better. Also keep in mind that If you plan to use the extra to amp channels to power music in a second zone, that will most likely only output an anaalog signal, so you would want to have your analog connection from the CD to receiver.
My guess is that the DAC's in the 525 would be superior to the Sony CD changer
