I have too TP-Link TL-WR740N/ND.
For System Link set port-triggering isn't needed.
You've set Forwarding -> Virtual Servers & UPnP correct.
In UPnP list Your XBOX should be listed active, for both opened ports and both, TCP & UTP, protocols (just like, in Your case, uTorrent is with 29558 port set and Torch with 51413 is). Check out UPnP list after XBOX reboot - XBOX on IP-address 192.168.0.100 with both opened ports (3071/3072) and both, TCP & UTP, protocols should be listed.
That's all You need to set on TP-Link TL-WR740N/ND for System Link availability.
But, besides that, Your ISP (or WAN-device like ADSL modem/router I have) should also permit traffic for both opened ports (3071/3072) and both, TCP & UTP, protocols, for IP-address dedicated to Your TP-Link TL-WR740N/ND.
You may also try to add XBOX IP-address 192.168.0.100 to Farwarding -> DMZ and check System Link availability afterwards.