Wow. this is a crazy long thread.
First, you wont be capturing to ProRes on a G5. Really need an Intel (Mac Pro) system to handle the conversion.
Second, you cannot do RAID 5 with your current setup. This requires dedicated hardware. Your options are either RAID 0 (what you have now) or RAID 1 (protection but no speed gain). You might be able to make some sort of RAID 0+1 (which eats half your total capacity for redundancy) for speed plus protection though I wont promise it would be stable especially since you are relying on the CPU to handle the RAID management.
Competent RAID 5 (or 6) storage systems use a dedicated hardware RAID controller. This can either be build into the chassis or be a card that sits in the computer and often uses a proprietary interconnect between the card and chassis.
The problems you are having with the drives now could be any number of things, a bad drive, problems in the enclosure, with the cables, or even the SATA card. If I was in this situation, I would start puling everything apart, blowing out any dust, checking internal connections, trying new SATA cables. Maybe even attempt to individually format each drive in a known valid setup to see if any drives are dead or perhaps something about the current state of the setup is locking up Disk Utility. I've definitely been there. Nothing works until you do something you shouldn't have to do and then everything is just fine.
I wouldn't try to add RAID 5 capability to your current setup. Could just be one nightmare on top of another and it sounds like you are in over you head already. I also wouldn't recommend you attempt any sort of roll your own setup but rather that you buy a complete system.
Two possibilities, the 8TB models will run between $5 or 6K:
http://www.caldigit.com/HDOne/
http://www.sonnettech.com/product/fusiondx800raid.html
Warning, many of these systems are very picky about card placement, system configuration, and OS versions. Make sure your setup is correct or you will have troubles.
Regarding your "nightmare" with Promax. For as much as this and other pro equipment costs, I've had plenty of problems with new out of the box gear over the years. It's just the nature of cutting edge technology. Don't plan on it working right on day one. It often does but it doesn't always. I personally had trouble with an above mentioned CalDigit HDOne. Futzed with it for a couple days, several exchanges with tech support, sent it back. the replacement dropped right in and went to work without a hitch and has been stable for months now.
