You can use whatever clock you want, as long it supports 44.1k rate. You can get a Puccini U-Clock, the older dCS Verona, one of the Esoteric offerings or even one of the studio clocks available, like the Apogee BigBen (~$1000 from ebay).
Effectivnes of using external clocks with single box CD players has always been questionable. I remember coments posted by another user on this forum a while back - he connected uber-expensive Esoteric Rubidium (Rb) clock to his Esoteric X-1 single box unit and also did not notice much of a difference.
Effectivnes of using external clocks with single box CD players has always been questionable. I remember coments posted by another user on this forum a while back - he connected uber-expensive Esoteric Rubidium (Rb) clock to his Esoteric X-1 single box unit and also did not notice much of a difference.