When talking about the great "Sound Of Joy" and "Sun Song", I would get the Japanese Mini LP versions or the vinyls for best sound. You should also check out the classic "Jazz In Silhouette". I also love the Evidence CD release of "When Angels Speak Of Love".
For many of the 50-60's records originally released on Saturn like "Art Forms Of Dimensions Tomorrow", "Cosmic Tones For Mental Therapy", "My Brother The Wind, Pt.1" and more, the sound are better on the vinyl releases from early 2000, IMHO. Shops like Honest Jon's and System Records in UK have these. The Evidence CD's has great liner notes though, and the "Greatest Hits" from 2000 is a great collection with good sound.
"Lanquidity", "Live In Montreux", "On Jupiter", "Sleeping Beauty" and "The Solar Myth Approach, Vol.1" and "The Solar Myth Approach, Vol.2" are also must-haves in my book. For the Solar Myth's the vinyls have the best sound.