If anyone wants to install Ubuntu on an old Mac Pro 1,1:
Use the 14.04 mac+amd64 iso for the installation, you can upgrade to 16.04 later and it works fine.
Install from a DVD, not a USB stick.
rEFInd is your friend.
You will probably need to boot from the live DVD and boot-repair.
It won't play nice with an OS X install on a partitioned drive, but a new hard drive or shared drive with windows works fine.
Disconnect the iSight camera before installing or you'll have no sound. No idea why.
Update: It was a Windows install DVD. I have now ordered some blank DVDs and an external DVD drive.
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