S4 + MHL / HDMI performance issues

[Elybear]

First post, please be kind~

I've recently purchased an Aibocn MHL to HDMI adapter for use with my S4 (SPH-L720 running 4.4.2) and there's been some odd issues when connecting to my Panasonic Viera television or my HK 1700 receiver using this dongle. The whole phone seems to slow down and applications (emulators, games, youtube) run choppy. I'd guess things are moving at about 20fps give or take and this immediately goes away once I disconnect the adapter. I've read some posts about Kit-Kat causing HDMI issues but they seemed to be related to functionality and not performance (i.e. things will completely stop working). Can someone get me started on troubleshooting this? I tried enabling the CPU monitor under dev options but the readout wasn't exactly user friendly. I can see process names and some 2.8/2.8/1.7 figures at the top while watching youtube if that is an indication of anything.

I should add that when playing video I encoded on my PC then moved to the SD card I don't have any perceivable issues aside from a little audio lag which is most likely my receiver. I don't know if this is because the CPU isn't struggling with this or because it's not an application which is having issues with HDMI. I tried turning the animations off and enabling forced GPU rendering which seemed to help a bit but not enough. Thanks for reading

 

[Elybear]

Today it was suggested to me that perhaps when an HDMI cable is connected the phone is rendering two copies of the image instead of just duplicating it to another screen. That may explain why when a video is played from the file browser and the main screen goes to an icon in front of a black background and the video is only played on the television the unit does not slow down. Is there a way to disable the main display so I'm only rendering 1080p instead of 1080p x2 which may be causing the issue?