Hmm which particular shields do you want to use.
If there is a conflict between shields wanting to use the same pins perhaps you could consider building your own shield that won't use
The motor shields I have seen, seem to use H Bridge driver IC's, which you can easily work with on your own even if you have to copy the schematic of the shield and modify it somewhat.
Otherwise option B could be to take two off the shelf shields, ie the motor shield and the sound shield and make your own adapter that reroutes the connections.
This adapter can be made from veroboard/stripboard and be made to be placed inbetween shields. It could be done with a bit of fiddling.