Do some reading - find a DAC that is reknown for jitter rejection and that accepts all the standard digital inputs (AES/EBU, S/PDIF, TOSLINK and now USB) and off you go - start auditioning for the sound style you like (all D to A converters will have subtle differences).
Unlike what Eric says - as long as your DAC is robust at jitter rejection then you can even consider an Airport Express or just about anything else which has less than stellar jitter performance.
Think about it - your source may likely change over the years - so apart from finding a DAC that you like the sound of - your biggest consideration should be to find one with as many inputs as possible and reputable jitter immunity...then just plug and play.
Unlike what Eric says - as long as your DAC is robust at jitter rejection then you can even consider an Airport Express or just about anything else which has less than stellar jitter performance.
Think about it - your source may likely change over the years - so apart from finding a DAC that you like the sound of - your biggest consideration should be to find one with as many inputs as possible and reputable jitter immunity...then just plug and play.