Primarily, we use Redbook 16bit / 44.1khz cd. Disc is read by the MBL 1621a, data then transmitted via our own 75 ohm digital interconnect to a Concert Fidelity DAC-040BD. This is pure unfiltered 16bit conversion, non up sampling, tube rectified (NOS Mullard 1958 6Ca4), tube analog output (currently running some lovely sounding NOS Mullard ECC 82 and Tesla ECC802s or Mazda 6189/12au7WA for classical). The analogue output stage is critical. Much enjoyment is had by experimenting with different tube combinations, with the nos 12au7 being the recommended tube by Concert Fidelity, we have used various Mullards, Mazda 6189’s, Dario Miniwatt 6189’s, RCA 5814 etc etc.. Check the Valve page for more info..