I have an older LW5700. I hacked into the service menu. I activated time machine, local dimming, THX Cinema Mode, THX Bright Room Mode and Dolby 5.1 Passthrough. Haven't tried time machine yet but as far as I know, uvax is right. Coax (cable) input and composite and lower quality input can be used with time machine. I haven't tried it yet but that is what is said in other forums.
If you wanna use time machine with your cable box, you might wanna try using its composite output.