Hi!
I too have Liquid Mix TDM.I asked this question to Focusrite Tech Support. Here their answer:
Unfortunately there is no scheduled plan to release a 64-bit version of the Liquid Mix HD plugin at the current time.
It might be something that is possibly implemented in the future. If you would like to get access to this before it is released then I would advise you to sign up to our beta site:
http://beta.focusrite.com
Sorry that I couldn't be of greater assistance.
Best regards,Joe Noel
Focusrite/Novation Tech Support