I too have this issue with using my Max Impact and running some heavy graphics apps. I have removed the internal drives and attempted to use external hdd pack, to find the same problem.
My PSU is the same as yours, suitable for Dual head impact R10k systems, but I don't think its upto snuff for the Max Impact? I think its 385W my current one, does anyone know what the Max Impact recommended psu's are rated at?
I have a dead I2 psu, which I am going to fix when I get some time, and change some caps, that may solve the problem, if not I am going to try to utilize a 500W atx corsair psu or something decent to replace the old I2 psu. That is going to require pinning out everything and be a real pain though. <sigh>.
Anyone have the pinouts for the Indigo2 psu already

?
I'm just worried about hearing the 'pop' sound of something in the power supply, and usually from experience with PC psu's the cheaper variety at least, that takes out your mobo, and hdd, etc as it seems to 'fry' them. Don't want that happening with my I2MI.