I do not own this game but I know about the mono problem Activison have fixed it
One draw back you will have to wait for activison to fix the prob and then they will send out a fixed version of the game for free
See the bellow quote for details
We recently became aware that some consumers have not been able to enjoy the full audio output in the Wii version of Guitar Hero III: Legends of Rock. We are currently working with Nintendo and are planning to issue an improved audio experience in future versions of the game. We expect to have re-mastered discs available by early 2008 and we will be offering consumers replacement discs at no cost once they become available. Should you have any further inquiries, please contact Activision customer support at http://www.activision.com/support. Customers based in North America wanting to pre-register for a free replacement disc can call (866) 780-8286 from 8:00am-8:00pm EST, Monday-Friday, and we will notify you once the replacement discs are available. We thank all of our customers for their support and patience.
If you wish to be notified by email as the information on this page is updated, please click the 'Notify Me by Email if this Answer is Updated' button. Please note- you must have an account with us to use this feature. If you do not have an account yet, you can create one by clicking the My Stuff tab and then 'Create a New Account'.