Yes, it's better to install OSX 10.10 Yosemite:
https://forums.macrumors.com/threads/os-x-yosemite-on-unsupported-macs-guide.1761432/
OSX 10.11 El Capitan is due to the System Integrity Protection and the USB-issue quite complicated.
The ATI X1600 works only half-way in OSX 10.10 Yosemite - without QuartzExtreme/CoreImage graphics acceleration and without OpenGL/OpenCL.
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The Installer hangs? Because the Input Devices don't work? Looks like the USB-issue.
In my experience the USB-Inject-All Kext works with a transferred OSX but not with a patched Installer.
Is it stable with a transferred OSX ? Last experience I had was KP after a few seconds
Thanks.