No I am not advising you build (it won't be a Mac)
You can't slap in new logicboard w/ Mountain Lion support (EFI64 is UEFI 2.x standard).
I am saying a Mac-Mini might let you use new software.
If you want to stay with the Mac Pro then I would look at 2009 ($1200) or later in used, or 2010 in Apple Store Specials ($1819)
Or search out the alternatives which are not endorsed or supported on various web sites and forums (but not Apple's).
Me? I run Windows 8 on mine. Windows PC parts and upgrades you can have a nice system
I just built one and the specs were huge improvement over what iMac or Mac-Mini for an under $1000 system.
cpu i5 3770 quad core 3.5GHz $220
GTX 660, $220
16GB DDR3 $100 (I had 3x4GB DDR3 from before)
$79 UEFI motherboard Gigabyte,
Windows 8 supports UEFI (my last Intel PC died after a firmware update I should have avoided.)
Copy of Windows 7 or 8
case and PSU $150-300
for $900 to $1,000
Add SSD and hard drives. Samsung 840 SSD $95, WD 1TB Black $90
Also if you want a higher end boards pay more. Same with processor.
When a new processor comes out, may need to just factor in $300 for cpu and $200 for motherboard probably. But you can't do that with Mac.
A 7 yr old system with 4 or 8-core like yours (and mine) still does what it would and more just not the iCandy and a rare 3rd party app. And I doubt someone can be selling an app that requires a Mac with 64-bit kernel only. You can run 64-bit apps.
ML opens up addressing more than 4GB of memory per task, not a must but does help CS6 users with huge files.
And I would not visit a site that req'd java (not just java script) and seems to have lots of torrent users and activation keys but that is your business and if it is what you need as the best tool for your business and music production which is out of my field.
Most software has had to deal with move away from PowerPC and Rosetta and away from "Carbon" coded apps to more Mac OS friendly and better code foundation and compliers.
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