You can try wrapping your waveformatconversionstream in a blockalignreductionstream before passing it to waveout, which might help. I still can't understand why you'd need to change blockalign for a-law. I use a-law all the time with NAudio and have never needed to do that. Your file has an asf extension, which suggests to me that there is more than just raw audio in the file.
As for sample rates, I suspect that windows is using another WaveFormatConversionStream under the hood to do SRC on the fly. This might account for some of the issues you have.