Basically its still the same tool, provided by firecore that does the jailbreaking. The instructions to install the nitoTV software center are also still valid, however the XBMC installation procedure is a little more difficult because the version provided by nitoTV is not yet compatible with the new iOS.
Fortunately the actual nightly build is quite stable and works as expected. To install it you need to connect to the ATV via SSH as you've done to install nitoTV and issue the following list of commands.
apt-get install wget wget -O- http://apt.awkwardtv.org/awkwardtv.pub | apt-key add - echo "deb http://apt.awkwardtv.org/ stable main" > /etc/apt/sources.list.d/awkwardtv.list echo "deb http://mirrors.xbmc.org/apt/atv2 ./" > /etc/apt/sources.list.d/xbmc.list apt-get update mkdir -p /Applications/AppleTV.app/Appliances apt-get install org.xbmc.xbmc-atv2 mkdir -p /Applications/XBMC.frappliance wget http://mirrors.xbmc.org/apt/atv2/deb/org.xbmc.xbmc-atv2_11.0-3_iphoneos-arm.deb dpkg -i org.xbmc.xbmc-atv2_11.0-3_iphoneos-arm.deb rm org.xbmc.xbmc-atv2_11.0-3_iphoneos-arm.deb apt-get install com.nito.nitotv apt-get install com.nito.updatebegone reboot
And that's it again. On the ATV's main screen there should be the well know XBMC-icon which starts your new media center.