With out seeing the hidden drop down menu items, it might be kind of hard to tell how to really configure this modem for QoS. Some of it looks fairly forward in Physical LAN port, Protocol, Source Subnet Mask, UDP/TCP Source Port, Destination IP address and subnet mask, I don't think you need Source and Destination MAC address, however not sure. Not what value to set for 802.1p. Some of these options are kind of close to ones listed on DIR series routers:
Gaming and QoS for XBLI would contact DLink support directly. Level 2 or higher. These are fairly complicated settings and needs someone to help configure them correctly and explain it. As a last resort, you might want to bridge this modem and install a external router that is more easier to use, something like a DIR series.
If you get any information and help and get this modem configured, please post another screen shot so we know what it looks like.
Please keep us posted.