What could cause such enormous smoke on the logic board that isn't visible from outside (nothing melted)?
If it's a Disk Utility software RAID, you can attach the drives whichever way you want (USB, FireWire, SATA) to any other Mac running the OS you had on your Mac Pro or later. The RAID set will work like on your Mac Pro – provided it hasn't been damaged by the logicboard dying.
What could cause such enormous smoke on the logic board that isn't visible from outside (nothing melted)?
Have any Electrical Engineering friends? You should check all capacitors with an ESR meter. One of my relatives was good at replacing capacitors on motherboards, dsl modems - all manner of electronics.
This website http://www.badcaps.net has a forum just about bad capacitors, and they have a repair service as well - though shipping might be expensive from Malaysia.
Capacitors may be bad w/o much visible damage.
Get a new board: http://www.ebay.pl/itm/GENUINE-APPL...ther_Computing_Networking&hash=item2576baa1dd
This one seems to be for 3,1 despite description.
Alright, I think I've made up my mind. I'll only repair it if the cost were below $350 or MAX 400 inclusive shipping. Anything more then that then I'm not repairing it. I will use the casing for a hackintosh project and maybe try to sell off the Xeons, FB-DIMM RAMs and build a nice i7-3930K rig and put it into that casing, which will easily beat the existing 5400 Xeons.
That's a good plan. Check out http://www.tonymacx86.com; I've built two Hackintoshes using this site. I also built one of them in a Power Mac G5 case (see sig). Tons of other forum members over there have done that, or used Mac Pro cases, too.
Thats what inspired me to do haha, i saw your sig PowerMac-i7 lol..