Furler woes...

[Brion Toss]

Welcome to Profurl hell. The drum, as it happens, is aluminum. The little sign saying "Titanium" refers to the blue screws. As near as I can tell, the engineers at Profurl wanted to use screws that were as far apart on the galvanic scale from aluminum as possible. And then they cleverly left suggesting isolating the metals out of the manual. You have already tried most of the tactics for this situation. One more might be to get a Makita cordless impact driver, and fit the appropriate metric allen head in it. This might take some doing, but it is an amazing tool for jobs like this. If that doesn't work, you will need to take the furler off the boat, get the drum off, and jig it up in a drill press. There are some Profurl dealers that are all-too-familiar with this procedure. My favorite is Pacific Offshore in San Diego.
When/if you get that screw out, be sure to put some Tef-Gel under the head and at the top of the shaft before putting it back in. Don't put it on the threads, though, as these need to engage the nylock inserts on the linkplates.
Fair leads,
Brion Toss