Well, I was just running 2 for proper and the other two for back-up I guess. However, every time I look at it it seems wrong, so I'm going back to just 2x 4TB HDD. As for you mentioning USB DAC, can you explain what they are because I have NEVER heard of it... I mean, what can be better than an actual dedicated sound card? As for the Watercooling, the H100i is the best Liquid Cooler there is in terms of temp, and I've been all over the place including the video from Linus doing the test of the H100i. Also, the Noctua fans are no longer thee best in terms of Temperature and Performance, not only that but the Phanteks Fans performs a lot better than Noctua with 200RPM less.
Here are some links:
http://www.silentpcreview.com/article1345-page7.html
http://www.overclockersclub.com/reviews/phenteks_f140/3.htm
I just changed to that, because before I was going to go with Noctua's because I thought they were the best until I looked around more and more I came across the Phanteks ones. Also, why would I need to change the OP AMPS as well? Need a little more explanation there. How many GPU's should you think I should be running for this sort of build? I thought 2 would be best.