The Antec HCG 620W is the Seasonic M12 620W. An older good design, with 80+ Bronze efficiency and quiet but audible (I have the Corsair branded version and ended up replacing the fan). In the US, it's selling for >$100. Your build will draw ~250-275W when completely stress loading the CPU and GPU. In normal operation (DAW work or gaming), it'll be closer to 200W. Some PSUs to consider (all 80+ Gold) in the same price range: Seasonic x 400 fanless, Seasonic x 560 (fan off until ~50% load), Seasonic G 550 (fan always on, but should be pretty quiet at your load). Another is the Kingwin LZP550 Platinum. Take a look at the Noise vs Power table on this page
Heatsink: might need to replace the fan for quieter operation.
GPU: This Windforce card isn't the quietest beast. Take a look at the Asus DC II or MSI PE Twin Frozr
At this point, the two HDDs will be the noisiest components. I don't know how fast the sample drive needs to be, but the WD Red 3TB
seems to be faster in some apps and quieter than the WD Black. The back up + video drive (assuming video is stored video for playback?) could be a quiet 5400rpm WD Green.