Hi,
The current exporter isn't properly exporting the opacity value of MAX materials. This will be fixed in the next version of the exporter which should be released in a few weeks.
For the time being, using one of Flare3D's old materials might do the trick. F3D Flat Color for example, has an Alpha value. You can also change the material alpha from Flare Studio if you have access to it.
Regards,