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
rebootAnd that's it again. On the ATV's main screen there should be the well know XBMC-icon which starts your new media center.
