If you like the Cary sound, why not sell the 303/300 and get one of the Cary units with digital inputs? 306SACD is nice, but 306/200 will do nicely also.
And there are mod outfits that can fit your 303/300 with either spdif input or USB input if you can't give up the SS vs. tube switching, though having heard both, I would stick with SS most of the time...