ok, I own an Wave 723 now, and i can say, WaveBackup works on that model also, with little limitations.
First of all, you have to make sure, TKFileExplorer mode is active.
->  Common
->  USB Configuration
->  TKFileExplorer – ON  (twice!)
-> # -> ‚Back‘
Problem is, the 723 does not answer to the normal AT commands, as the Wave I does. You can activate AT Commands in the service menu, but the it seems TkFileexplorer does not work anymore …. so, when using wavebackup, after making connection, you’ll have no confirmation of connected device, but file explorer and backup should work fine.
I guess this will be the case for other wave family models too!