I might have been a bit hasty in jumping into multi-arch. It is not fully formed yet in Debian and it is not straight forward. Definitely OK for the curious pioneers if they want, mine is fully functional as an AMD64 system but not too sure it is properly configured as multi-arch. Ubuntu seems setup already if you install 64bit. More research required.
EDIT: My system got hosed by a conflict between my Samsung Laser drivers and system updates. I now know how to fix it without trashing everything, but alas too late for the initial trashing. I installed from a debian multiarch netinst and it all went well, but somehow I managed to convert it to a conventional AMD64 with ia32-libs and ia32-libs-gtk. Never mind as it works fine, it is just not what I intended. I then added all the Mint bits to create a hybrid Mint/Sid system that this forum is all about.
Any Debian super stars out there who know about multiarch feel free to comment. I guess the other issue is the Mint LMDE repos are not multiarch yet.