I'm using sox to convert audio files to a specific wav format required by a game, but am not finding success.

The only difference I can see is the block size - the original game audio uses blocks of 256 bytes, whilst sox produces files using 2048 bytes.

My uneducated guess here is that the game is using Microsoft's library for decoding:
https://msdn.microsoft.com/en-us/library/windows/desktop/ee415711%28v=vs.85%29.aspx

This specifies a maximum allowed SamplesPerBlock of 512 - with a block size of 2048 bytes, the file has 2036 samples per block.

Is there a way to specify block size when converting to ADPCM? I tried several -C numbers but it doesn't seem to be used for ADPCM.