I just pushed through some new code which should make life easier. Although everything will still work as it did before, I'd now recommend using a folder called Assets/CsoundFiles to hold all files Csound will be reading. These can be anything from audio files to text files. All files in this folder can be accessed using the CsoundFiles channel, e.g.,
SDataPath chnget "CsoundFiles" ;path to Csound files...
SDatfile sprintf "%s/test.dat", SDataPath
gihand fiopen SDatfile, 1
SFilename sprintf "%s/skipmixmono.wav", SDataPath
a1 diskin2 SFilename, 1, 0, 1
outs a1, a1
When you create a standalone build of your game, the PreBuildScript.cs will copy all the files from this folder to the StreamingAssets folder. It will also update the CsoundFiles channel so it now points to the new location of the files. If you work with an Assets/CsoundFiles folder you won't need to do anything when creating a standalone.
I'd like to get Unity to exclude the Assets/CsoundFiles folder when building but I haven't managed to do that. Although Unity will try to compress everything in this folder when it creates a standalone, we don't need any of it. It just takes up space. The only solution I found thus far was to create a standalone from the command line. If users are creating scenes with lots and lots of audio files specifically for Csound this would be a better approach.
I'll update the docs now to reflect this new addition.
 I just realised that the .csd files are in a folder called CsoundFiles too. Anyone have any objections if I changed this folder name to CsoundInstruments?