Running Cubase 6.5 64 bit here on OSX Mountain Lion 10.8 on a MacPro
Hardware inserts work just fine in 64 bit in Cubase, I just checked my Lexi and TC for you.
1. Have you setup your VST Connections to add the external effect buss
2. Have you assigned your audio I/O box as the driver
3. Have you selected the outputs for the send
4. Have you selected the inputs for the return
5. Have you checked your cable connections to make sure they are matching the software
6. Have you then tried inserting the EXT EFFECT on a track
7. Or, have you added an EFFECTS track and inserted the External effect on that track and turned up the send on an audio track going to the effect unit after you selected the proper send
8. Have you checked you input and output settings on your external device
9. What I/O are you using?
Logic X 10.06, Cubase 7.5.20, StudioOnePro 2.6.2