So sorry to trouble you.
I'm sorry it's not working.
I stepped the code in the debugger, and understand better now. W64 is slightly different than a traditional WAV (it's official name is "Sony Pictures Digital Wave 64").
So our native WAV handler does not like W64, and lets LAV decode the file. On my machine, this works (but won't be bit-perfect @ 64-bit). I'm not sure why that doesn't work for you, but it doesn't really matter.
I'm working to add native W64 support. If things go well, I should be be able to post a test build for you in a day or two.
Thanks for your help on this.