Well, if it works with iMovie '08 it should certainly work for iMovie HD 6.
I'm not at my editing Mac at the moment, so I can't check some of the differences between the two versions of iMovie. But perhaps you can 'reset' iMovie HD 6 by using the Finder on your Mac to go to the following folder: <your Home folder>/Library/Preferences and then remove the file called "com.apple.iMovie.plist" and put it in the Trash.
(..The next time you start iMovie Hd 6 it'll rebuild this preference file, so don't worry..)
It might also be that you have some QuickTime plug-in which is interfering with capture from the camcorder, so check in the folder called <the name of your hard disc>/Library/QuickTime. You should see "AppleIntermediateCodec.component" there. But if there are any other weird codecs, temporarily remove them to somewhere else, then restart the Mac.
Early versions of 'Flip4Mac' (..a plug-in to allow QuickTime to play back Windows files..) can interfere with QuickTime and iMovie, as can some others.
Apart from those items, I can't think why your Sony can import into iM'08 but not into iMHD6.
Sonys are usually well-behaved and work perfectly with iMovie ..especially as yours is a
tape-based DV/DVCAM/HDV model, and that's what iMovie was designed for!
The only thing which may make your camera incompatible with iMHD6 is that iMovie 6 may not properly import any
progressive footage you may have shot, but it should work perfectly with normal DV, with DVCAM and with HDV.
But make sure that you select the correct kind of new project before trying to import: when creating a new project, click on the little right-pointing triangle next to 'Video format'..
..and then choose the correct type of project for the material you've shot:
(..Note that you should choose DV or DV Widescreen - depending whether it's 4:3 or 16:9 shape - for material shot in DVCAM mode. DVCAM is identical to normal DV, except that the tape runs faster through the camera to produce wider tracks on the tape, making the recordings more robust and more compatible with other hardware ..as 'professional' material is usually edited on different machines from the ones which actually shot the video..)
And as you've got an 'E' version (European) camera, make sure that you choose the correct frame rate in your iMovie Preferences. Your camera shoots at 25fps (PAL) instead of American 29.97fps (NTSC).
See if any of that helps, as you're certain that you've got the correct cable..