Currently as of FCP v5, Real Time Analog Video Pass-Through over FireWire does not work for HDV as it does with Standard Definition DV... it has to do with the GOP (Group Of Pictures) and the significantly greater CPU processing power required to process the HDV stream. The only time you can send an HDV signal back through an HDV camcorder via FireWire is when you go to the "File" Menu and then select "Print To Video". Final Cut Pro will then need a short amount of time to re-conform the media on the timeline (recreate the GOP) and then the timeline is ready to be "printed back to video" - essentially meaning the timeline is ready to be displayed without dropping frames over FireWire into the HDV camcorder, where you will then be able to record the HDV signal to tape and/or pull the signal off of the Analog video outputs of the camcorder as the "Print To Video" process occurs and display it on an Analog monitor (Composite, S-Video or Component).
NOTE: You must specify in the "Audio/Video Settings" within Final Cut Pro whether you are outputting 60i or 24Frame material when using a Canon HDV camcorder. You can do this by going to the "Final Cut Pro" Menu, then select "Audio/Video Settings", then click on the "A/V Devices" tab, then make sure that the correct selection is chosen under "Video" under the "Different Outputs For Edit To Tape/ Print To Video". Example: For 60i HDV, you would select "HDV (1440x1080) 60i". This will only be available if a FireWire cable is properly connected between your Canon XH or XL camcorder and your Macintosh. If you have an older or slower Mac, uncheck the "Mirror On Desktop" feature (provided that you have a monitor connected to your camcorder).
Please let us know if you need any further clarification on this matter and do keep in touch.