I think it's generally agreed that modern A/D converters sound significantly better than the earliest ones. Whether this is due to jitter is open to debate but something changed for the better. I have a few early digital recordings that sound atrocious and it isn't just the EQ. They are shining examples of poor digital transfer. It doesn't matter what kind of DAC I play them through - they still sound gritty and brittle.
This phenomenon was one of the reasons that the remastering business took off fairly soon after the CD was released. One example is HDCD releases. Pacific Microsonics made the A/D converters that allowed HDCD encoding as an option. These converters were considered a substantial leap forward and were felt my many studios to be the best available at the time (they are still used by some studios). Some HDCD collectors, myself included, feel that one of the main reasons HDCD remastered discs sound better than their original releases is that the converters were so much better. The HDCD encoding is icing on the cake.