In your firestick or android box Clcik search

Type in Mx Player

You will see MX Player.

Download the MX Player and install it. Then close the window no need to open it.

Open the slacker App

Open the menu panel

Iptv Menu On The Bottom.

Go to settings.

Then playback

Scroll down to choose external player for individual channels

Pick the MX player from the drop down

Pick your channels from the list that pops up