The pack consists of a Audio CD with about 30 spectrum games (each one recorded twice), and a connection cable (cd player's 3.5mm (or 6.3mm via adapter) stereo headphone socket to spectrum 9pin DSUB joystick port) (for Spectrum 128/+2/+3 or 48K with Kempston interface), and loading software on tape, once when a game is loaded one can press Q,U,I,T on keyboard to load a new game (without needing to load tape loader again).
No info if/how the stereo signal is used (maybe one channel used as CLOCK, and the other channel as DATA...?) The cable does reportedly contain a 1bit A/D converter, which is probably a single transistor or so (so it's mono, not stereo?). The CD capacity is said to be "12 Megs" (presumably meaning 12 Megabit = 60 tracks with 25Kbytes each).