Hi Oreomambo,
Follow your guides, I managed to setup the RB750 & RB750G with both internet & IPTV working, thank you bro !!
Luckily MikroTik has the WinBox GUI, lots of features & information, otherwise I don't think I'm capable to configure it at command lines ...
The setup is rather straight forward, just few setup screen out of the box:
Interface – create vlan 500 & 600
[attachmentid=1810001]
Interface – set LAN5 neither master nor slave [to use for IPTV STB direct connection]
[attachmentid=1810003]
Bridge – create a bridge for IPTV
[attachmentid=1810006]
Bridge – Ports for IPTV bridge
[attachmentid=1810008]
PPP – Create PPPoE client for UniFi
[attachmentid=1810011]
Firewall – setup NAT
[attachmentid=1810015]
IP – DHCP server
[attachmentid=1810017]
That's all, internet & IPTV up & running!
Now have to figure out how to tighten the firewall ...

May I know, do you still ur TP-Link wireless router to connect ur PC / Laptop via RB750G? Or direct connect your PC / Laptop to RB750G?