Saya ada jumpa app bernama Secure Settings kt Play Store dan boleh install. Lepas tu, saya ada terjumpa setting untuk 'enable unknown' , tetapi dia memerlukan helper apk. Selepas flash-install helper tu, dah boleh enable, tapi macam tak ada effect lak. Sigh..... Ingatkan dapat la unlock unknown sources tu.

P/S : Lepas ni nak try modify build.prop dia la. Bole la dapat lagi byk app support kt Play Store.

I do managed to flash install MX Player on the decoder. Install the codec as well and you have one of the best video player running in your decoder. I used Aptoid to install it BTW.

Sorry for the late reply as I have been working and only at home at night.
Allow me to try and give you the simplest solution for the problem.

The simplest way to do that will be installing an app called Aptoide on your decoder. This will allow you to install many application that could not be found by using google play store.
The installer file can be obtained through here.
Here is my step on installing the Aptoide and then installs other apps.

1. Download the zip file and put it inside your pendrive. Your pendrive must be formatted as FAT/FAT32 or it will not work. (Mine is 8GB FAT32)

2. Plug-in your pendrive into the USB port behind the decoder.

3. Turn on the decoder with the ON button behind the decoder (NOT in the front) while holding the red ON button on the remote control. Hold it until it enters recovery mode.

4. After entering recovery mode, choose "Install update from external storage". Then choose the zip file that you have put inside the pendrive.

5. Let it install for awhile. After successfully installed, it will restart by itself.

6. After restart. go to "My Application" menu and you should see Aptoide app icon. Open it, find and install ES File Explorer and MX Player.

7. Open the MX Player. The app will prompt you to download the codec. Accept it and then choose to open with Aptoide. Install the decoder and then you have a working MX Player.

There you have it. If you have successfully follow these steps, then you will have a free media player for your home that are able to play almost all format with no hassle (It is able to play 1080p videos). You can also install other app such as music player or youtube player to increase the experience of using your decoder through Aptoide.

Well, that's it from me. I hope that this guide helps some people in installing their own apps in their decoder. I'm off.
Ciou~~

I'm not really sure as I had already rooted my decoder before installing Aptoide but AFAIK, you do not need to have root to install and run Aptoide.