I downloaded and installed the Coolux codecs for Quicktime, so I'm able to export to Coolux PNG with Alpha using Quicktime 7 on Mac.
Unfortunately I'm not able to directly play exported files to check them. Quicktime has convert them somehow, then plays them, but without Alpha channel. So I can't check the files before loading them into PB and spreading them on the site, which is time consuming and extremely awkward.