Mark,
I just discovered something and would like to share it with you and other K-01/K-03 owners out there.
Apparently the K-01 has a built-in USB to SPDIF converter. If you go to the Digital Out menu and choose THRU, the player cnverts the usb signal to spdif before routing it to the DAC.
I tried it and find the sonics way better than before. Since you have the Bel Canto Ref link, you can compare with and without it in the chain.
On a related note, playing music from an ultra fast SD card in the SD slot sounds better than from the computer's own hard disk or from a Usb thumbdrive in a usb port.
Also, if you use JRiver, Wasapi - Event style is the best output mode setting.
Happy listening!