Well....if your device is rooted there is the harder way to get custom notification sounds. I think maybe the app Ring Droid allows you to assign custom ringtones but IDK if it can assign notification sounds. If you are referring to the general UI sounds....than you'll probably have to be rooted so you can use an app like Root Explorer to manually set the sound files in place (I think they have to be in the. ogg format) and set permissions accordingly.
I suggest you check out the XDA-developer forums as they have a wealth of knowledge and friendly individuals to help you out with that specific device 
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