How to tether a 2014 MacBook Pro 15" Retina to two Dell Ultra HD 4k 27-Inch Screen LED-Lit Monitors (P2715Q)? I've attempted to connect my 2014 MacBook Pro 15" Retina laptop to two, 27" Dell Ultra HD 4k screens via OWC Thunderbolt 2 Dock, however, I was only able to tether one Dell screen instead of two; I've tried several combinations, which include the following:


MacBook > Thunderbolt > [OWC](HDMI to Dell_1 + Thunderbolt to Dell_2)
MacBook > HDMI > [OWC](Thunderbolt to Dell_1 + Thunderbolt to Dell_2)
MacBook > Thunderbolt > [OWC](Thunderbolt to Dell_1)+(HDMI from Dell_1 to Dell_2)


Apparently, Hengedock would be a great solution for tethering two 27" Apple Retina displays but I don't think the Hengedock is compatible with subject Dell monitors; I'm currently standing-by for my inquiry placed with customer-service.  I'd appreciate any insight or recommendations for OWC, Hengedock, or any other successful implementations-thank you!
It doesn't appear that your MBP is capable of driving 2 4k displays with the Macbook's primary display working (see Graphics and Video support):

https://support.apple.com/kb/SP704?locale=en_US

Also the OWC Dock isn't capable of driving 2 4k displays so even if your MBP is capable of driving the displays you'll need to use the HDMI port or one of the other Thunderbolt 2 ports to drive the second display:

http://www.owcdigital.com/products/thunderbolt/thunderbolt-2-dock-overview

One thing you may be able to try is to close the Macbook to turn off it's primary display, thus freeing up resources to try to handle both 4k displays.