I don't know if DATs could have side-band lyrics, but regular CDs had that in the spec. Regular CDs also had previsions for quadraphonic sound with half the running time in the Red Book, but no one ever made a player which would read it.
DATs ran at a sampling rate of 48 kHz, rather than 44.1. DVDs support stereo LPCM @ 48 kHz, but with 24-bit samples. So DATs don't quite reach the max of DVD quality, but come close.
There was a Digital Compact Cassette (DCC), which used 1/4" tape just like the analog compact cassette tape, but was single sided (think like a VHS tape which doesn't have the holes all the way through). DCC players were backward compatible with the double sided analog cassettes. They used a lossy compression scheme (predating MP3). The biggest competitor was Sony's Mini-Disc (also lossy, using ATRAC encoding).
