Triple external display support via DP/HDMI/DVI feature no longer available for Linux?

[QFang1]

Over a year ago, I was able to simultaneously use 3 external displays from my Linux desktop (Ubuntu 14.04), running on a i7-6700K (HD530 graphics) CPU. I have 3 monitors, connecting an LG ultra-wide 3440x1440@60Hz via DP, connecting a Dell 1920x1200@60Hz via HDMI, and connecting a Sony TV (native resolution is 4k) at 4k or 1920x1080@30Hz using DVI (through a DVI->HDMI converter). 

However, after I upgraded the CPU from 6700K to 7700K (HD630), with the intel graphics driver in the Linux kernel (4.3 series and 4.4 series), I was not able to get the 3rd video output (to the Sony TV via DVI) anymore. I recently upgraded my Linux to 16.04 and the kernel from 4.4 to 4.15 (using HWE kernel line), and was hoping that I can get the 3rd display back, but still, xrandr -q does not show me the 3rd output even it is connected. However, according to this page, 3-display is supposed to be supported for HD630

https://www.intel.com/content/www/us/en/support/articles/000025672/graphics-drivers.html

I am wondering if Intel dropped the support for triple external display support on Linux? if not, what is the correct kernel version that supports this? or this is an hardware limitation (630 vs 530?) I also reported this to Ubuntu as a bug, but there was no reply or activity

https://bugs.launchpad.net/ubuntu/+source/xserver-xorg-video-intel/+bug/1764924

any suggestions?

My current xrandr -q output is listed below:

fangq@taote:~$ xrandr -q
Screen 0: minimum 320 x 200, current 5360 x 1440, maximum 8192 x 8192
DP1 connected primary 3440x1440+1920+0 (normal left inverted right x axis y axis) 800mm x 335mm
   3440x1440     59.97*+  49.99    29.99  
   2560x1080     60.00  
   1920x1080     60.00    59.94  
   1680x1050     59.95  
   1600x900      60.00  
   1280x1024     60.02  
   1280x800      59.81  
   1152x864      59.97  
   1280x720      60.00    59.94  
   1024x768      60.00  
   800x600       60.32  
   720x480       60.00    59.94  
   640x480       60.00    59.94  
HDMI1 disconnected (normal left inverted right x axis y axis)
HDMI2 connected 1920x1200+0+0 (normal left inverted right x axis y axis) 518mm x 324mm
   1920x1200     59.95*+
   1920x1080     60.00    50.00    59.94    30.00    25.00    24.00    29.97    23.98  
   1920x1080i    60.00    50.00    59.94  
   1600x1200     60.00  
   1280x1024     75.02    60.02  
   1152x864      75.00  
   1280x720      60.00    50.00    59.94  
   1024x768      75.03    60.00  
   800x600       75.00    60.32  
   720x576       50.00  
   720x576i      50.00  
   720x480       60.00    59.94  
   720x480i      60.00    59.94  
   640x480       75.00    60.00    59.94  
   720x400       70.08  
HDMI3 disconnected (normal left inverted right x axis y axis)