I think the answers here will be to buy a DAC and use the Marantz as the transport..that's what I would do. (For $700 you would not make a significant upgrade with a new CDP).
Try looking thru the archives for opinions on a new DAC; the forum is full of DAC threads. For a tube DAC at a good price take a look at the Jolida.
http://www.musicdirect.com/p-106207-jolida-glass-fx-tube-dac-ii.aspx
Try looking thru the archives for opinions on a new DAC; the forum is full of DAC threads. For a tube DAC at a good price take a look at the Jolida.
http://www.musicdirect.com/p-106207-jolida-glass-fx-tube-dac-ii.aspx