Where there is a will ...
There is a way!
I got Mavericks installed natively on my old 2006 Pro, and it runs great. Everything works, and now I can easily get a few more years out of it. Apple doesn't support running any OS newer than OS X Lion on my model Mac Pro, and in the installation program for Mavericks, it explicitly checks the machine's model against a list of supported models. If your machine isn't on the list, then it refuses to install. I knew I could install it by connecting my machine to a compatible model with FireWire, and install it that way, but it still wouldn't run because the EFI built in the machine was 32 bit, and Maverics requires a 64 bit EFI to run. Well, after searching the internet, I came across several methods of performing this install using an alternate bootloader called Chameleon, but that install was pretty cumbersome, and required a small dedicated drive for the bootloader and installation software. Reviews I read indicated that though it worked, it had issues. I didn't want to go this route, and was considering buying a newer model that would support Mavericks directly. Then I read an article about installing on my model without having to jump through so many hoops, and from revies, it was stable as a rock and didn't break anything. All I needed extra to do it was a replacement BOOT.EFI program to replace the one in Mavericks, and I would be good to go. I downloaded the new module and below is how I did it:
On my Mac Pro I have three internal drives:, 1 250 GB HHD, 1 128 GB SSD, and one 1 TB HHD. I wiped my 250 GB Boot Camp volume, since I run Windows in a VM, and didn't really need it. Then I connected my Pro to my MacBook Pro via FireWire and booted the Pro into Target Mode. My MBP is Mavericks compatible, so I booted it and my Pro's disk volumes appeared on the MBP's desktop as external drives. I ran the Mavericks installer and <span class="text_exposed_show">used the 250 GB volume as the destination drive. When the installer finished, and wanted to reboot, I made sure the MBP booted from it's own disk instead of the newly created volume. I replaced a file called boot.efi in two locations on the new volume with one that was modified to work on the old Pro. Then I shut down both machines and rebooted the Pro normally making sure to boot from the new Mavericks drive. It came up and runs like a champ. I used Migration assistant to copy all my settings and apps from my Lion disk, and it all runs perfectly.
Then, being a glutton for punishment that I am, I decided to combine the 128 GB SSD and the 1 TB HDD into a Fusion drive. After I successfully created the Fusion volume, I used Carbon Copy Cloner to move Mavericks from the 250 GB HHD to the Fusion volume. Now it is REALLY fast. I kept the old Mavericks disk to use as an emergency boot device in case of emergency.</span>