For your suggestion, I would say TOSLINK (@24/192) to MSCALER input has the best chance of sounding most transparent, pragmatically speaking, due to the optical galvanic isolation and avoidance of whatever noise the Amanero is adding to the mix.
I hope at this stage of the game, we all understand that the integrity of the bitstream remains intact regardless of upstream sources or re-clocking. Some DACs (notably PS Audio and MSB) provide bit-perfect source 'music' files to let users validate that their upstream processing chain does not...
The intent of SRC-DX is to have the DAC turn off its USB receiver/chip & logic ...which also turns off the multiple clocks required. S/PDIF is a self-clocking protocol and inherently less noisy to decode than USB. So the entire process has a lower RF noise profile. You should hear benefit with...