Well, to use the 510 as a transport, just use a digital output into the Cal Audio Alpha. Output voltage level should not be a factor, since that is a function of the DAC, not the transport. It is certainly worth a try before you spring for a new transport.
I own a CDR-632 Marantz recorder, and I'd love to hear your results with the 510 as transport. If you feel the results compare well to the Cal Audio transport, I might be tempted to try my Marantz with a DAC.
FWIW, scratchy sound can come from a host of things, including source components, bad speaker cables, interconnects, dirty volume pots, etc.
I own a CDR-632 Marantz recorder, and I'd love to hear your results with the 510 as transport. If you feel the results compare well to the Cal Audio transport, I might be tempted to try my Marantz with a DAC.
FWIW, scratchy sound can come from a host of things, including source components, bad speaker cables, interconnects, dirty volume pots, etc.