DSD = Direct Stream Digital, 1bit and usually 2.8mhz, but can be higher. DSD is the recording method that is used for SACD's as PCM is the method used for DVD-Audio and CD's. Not many recordings have been made in DSD. Most SACD's would have had the original recordings remastered to DSD, but to my ears a DSD recording sounds better than the PCM equivalent, e.g. I used to think my DVD-Audio remaster of Rumours by Fleetwood Mac was excellent (24bit 96kz), then I bought the
Japanese SACD version, massive improvement in every respect.
Most studio recordings would be in PCM 24bit and varying khz, but not usually more than 192khz..
With regard to a DAC, it will depend on the sound character you're looking for. I auditioned the Rega DAC and Audiolab M-DAC at home. For me the Rega was the right choice having a more analogue sound with good bass. That matched my other kit well, i.e. the Monitor Audio speakers are quite revealing. In a less revealing set-up amp and speaker wise, the M-DAC may be your preference.