As above. Go to your "Now Playing" list; then press the "enter/last" button on the remote and up will pop, among other things, the option to turn groups on/off. Incidentally, you can apparently also toggle between groups being on or off by hitting the number 2 button on the remote as well. Never tried it as I leave groups on pretty much all the time!!
"It is useless to attempt to reason a man out of what he was never reasoned into." — most commonly attributed to Jonathan Swift, author/theologian