> do you mean full PCM or just some multi-bit for the DAC ?
There's no (easy) way to do volume attenuation in DSD or multi-bit. So DSD has to be converted to PCM in the first place.
> is there any difference of going from full PCM to some multi-bits (not sure if this is true) and going from 1-bit DSD to multi-bits ?
answered above. unless you use dsd direct (no volume adjustment), all DSD has to be converted to PCM first. Then magic (oversampling/sigma-delta) happens after that. Refer to chips datasheet.
>So my point was if it is possible to do this oversampling externally and make the DAC work without oversampling filters.
you can choose nos filter but it's not available at higher sample rates. See manual "At sample rates higher than 192 kHz DA Filter selection is no longer available. The DAC then uses a fixed Slow filter." Also, disabling the dac filter (NOS) and doing it on your computer will not give you better result ---- DAC's own oversampling can do it at a much higher rate (256x for AKM4493, for instance) and achieve better result, while your computer will struggle upsampling at such high rate.
> Also I missed the page in the manual for DSP limitations (just received the DAC yesterday), thanks for that. So for this discussion I can say externally upsampled up to 384kHz when I want to use something from the DSP.
MC confirmed in another thread that the RME TotalMix FX technology will upsample your signal internally. So both DSP and DAC chip will do the upsampling work for you.
If you upsample it to 384khz and send it to the dac, the dac will then apply another filter to upsample it anyway, as mentioned above.