find the gear icon (setting), there should be network setup then u can disable ur wifi and enable your ethernet.

have u to change cable or to change to a different port?

For my case i had tried both but still faint.. i suspect my NIC failed. So no lan for me.. only Wifi.. 

if u have ethernet connection, use it... it's better.
unifitv lan cable port is port #4 - this is ONLY for unifi tv, cannot use for other purpose.
use port 1, 2, 3 for all other internet connections.

if u fail to connect with ethernet, go to settings, more, ethernet and see what is there.
typical fault is ip address - for TM router, need to set to 192.168.0.1 whereas other routers need to be 192.168.1.1
change accordingly/save, power off, on again, u will get connected.
then u can decide to keep using hdcp or static ip; decide if u want to use auto assigned DNS or some other DNS.
just play with it, u will learn... like i did... long time ago.

1. No surprise... the free stuff, free apps inevitably die or eed updates, need new apps.
2. Firmware too old, out of date, buggy.. need to update firmware.
3. The preinstalled youtube is not update... just ignore it. Install new version.

Your case, best to take it to a shop which sell himedia. May need to pay a bit... a bit of work required.

the hardware of this box is good.

the rca audio output should be as best as it can be.

so, i doubt DAC will improve the quality.