Resolution Audio Opus 21 (4XPCM1704 R2R ladder d/a converters).Hmmm very nice, last "best" (PCM1704) of the R2R ladder dacs before the discrete ones.
There is one on Agon for sale https://www.audiogon.com/listings/lisa3dch-resolution-audio-opus-21-system-cd-sacd-players
And there are a couple for sale on hifi shark https://www.hifishark.com/search?q=opus+21
Cheers George