Can anyone explain to me briefly the theoretical and actual advantages of this dac (if any)? Other than a $6000 Price tag I can decipher little.
There are none, this is just
FUD. There is nothing deeply hidden in digital audio files.
Regarding the different formats it makes sense to convert PCM data with a DAC able to convert PCM, and DSD data with a DAC able to convert DSD. Just doing a software conversion from PCM to DSD will not improve the quality of the signal, but
when done wrong may degrade it. The same is true for the other direction.
I would just interpret this sentence different:
Imagine going to a recording studio and listening to a master tape of any recording made. There is no need to go into a recording studio - just buy the equipment the pros use in the studio. You won't find PS-Audio there, but look for names like MOTU, RME, ANTELOPE, etc. This is no nonsense stuff with a price/quality relation difficult to beat.
Since you already asked for the RME: Let us know what you really need and I'm sure you will get some good recommendations for equipment which measures good and is not overpriced.