Joe has several high resolution audio downloads and would like to burn them to CD. He has an SACD player and also a DVD-A player, but he doesn't have a high resolution player like the Pono. Leo says that SACD and DVD audio were two formats created to deliver higher quality than CD. In most cases, it was for surround sound and other features, but it could be higher bit rate. But unless he could make that CD, the fact that he can play it back doesn't really help him here.
Yes he can play the CD's he already owns. It just comes with a CD player that can play DVD Audio. There are two higher quality formats that never really took off. One is SA-CD, and the other is DVD Audio. Both are capable of 5.1 surround and much higher bitrate audio. There aren't many CDs or DVDs in that format, however. He still would benefit from having a higher end sound system, and he could even buy a DVD Audio disc to try it. One place to check for them would be Amazon. They have a whole category for DVD Audio.