It seems like the Wii's version of Guitar Hero 3 is a huge step down from the PS3 or Xbox 360 versions. Not only does it not have an offline co-op mode, it seems to be having some sound issues. The game refuses to output sound in any mode other than mono, even though it's advertised as supporting Dolby Pro Logic II.
If it weren't bad enough that Activision shipped out Guitar Hero III with no offline co-op quickplay mode, a few careful listeners have noticed another thing they left out - a few channels of sound.
Audiophilic owners of Guitar Hero III for the Wii have noticed that not only does the game not support Dolby Pro Logic II surround sound systems (despite that feature being advertised), but it doesn't even output sound in stereo. As we all know, it's nearly impossible to pass "Cult of Personality" on Expert unless the manic shredding of Living Colour guitarist Vernon Reid washes over you from six different angles.