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You might need to check with Dell if this configuration is possible for your computer model. From my end, I can start by saying that Intel recommends straight connections only; according to the specification for the 4th generation processors you will be able to achieve the following display configurations;
See line 6 in the table, based on this your graphics controller should be able to achieve 3840x2160 @ 60 Hz using the eDP and the DP.
For further reference; Intel® Core™ Processors (M/H-Processor Lines) Datasheet, Vol. 1.
Thank you for your reply Amy. I contacted Alienware/Dell tech support before posting this and their reply was no it can't because it's only on DP connector which to me meant there was a lack of understanding that the DP spec allows for more that one display to hang off of a DP output. I am not using the internal display on the laptop when the two external monitors are in use so I'm not sure if that means the bandwidth allocated to the eDP is then available for external DP connections. I found this on the VESA website which is what prompted the question:
If you scroll to page 13 you can see an example of a DP 1.2 hub making use of the MST to support multiple monitors from one DP source but there is no mention of display resolution or refresh rate with that visual. The tables on pgs 18 & 19 would seem to indicate that you can only connect one 4K external display using DP but again, I'm not using the internal display so wasn't sure if that freed up any bandwidth for a second display. Sounds like the answer is it does not.
In general terms, the total amount of displays supported depends on the resolution, refresh rate and color depth set for each display along with the available bandwidth per each DisplayPort output. DisplayPort 1.2 max effective bandwidth for each DisplayPort 1.2 output is approximately 17.28 Gbps. Note: Standard is defined as 21.6 Gbps, but this is reduced due to necessary overhead.
One display at 4K@60hz takes approximately 15.93 Gbps in bandwidth, thus limiting the number of Displays at 4k@60hz on each physical ports to only 1. Onboard GPU also establishes a max # of supported displays. Haswell, Broadwell and Skylake familiies support a max 3 simultaneous displays.