PS: I ask Daniel Coulom for a tool to convert .k7 to .wav format (tape). For the opposite way exist a tool.
Thanks goes to Yo_fr (the developer of the MESS driver) to send me a .wav files for testing.
He made a tool to convert K7 to WAV format, maybe he can help to add in castool.
Game : Formule 1 (Tape)
Game : Stramble (High resolution, Tape)