The effect of source and external "double DACs"?

There is no "over-dac" effect because if you use the digital output of a cd player is bypasses the internal dac. A cd player can make a perfectly fine transport, a dedicated transport may be better but likely significantly more expensive.

My Meridian MS600 endpoint up-samples native 44.1 kHz files to 88.2 kHz and applies an apodizing filter before outputting a digital signal via coax S/PDIF to my Simaudio 650D dac. So this is not double dac per se but there is some processing of the digital signal before the final dac processing. Thoughts on this?

If I might add a question of my own:

Would it be totally crazy to A) Run an optical out from a TV (only optical out for digital) to a DAC in order to utilize the coax digital out from the DAC since, in this case, the coax digital cable is much, much higher quality than the optical cable? B) That high quality coax digital cable would would then run into an integrated amp
with a DAC...

Scratch that question: my DAC does not have a digital out.

: (