I think the depth problem will be a challenge with most cases made
for mixers. The best working solution will probably be a Portable
case and a stand to make it lean back at the angle you want. There
are some good acoustic guitar stands that work well for the portable
cases. Ones with this type of design:
http://www.amazon.com/gp/product/B000JC495Q
or this
http://www.jcpenney.com/jcp/X6.aspx
DeptID=58200&CatID=58200&Grptyp=PRD&ItemId=1352a54

both for under $20.

-James