when I import an .mts file with 8 bit grayscale.jpg transparency maps in StreamTuningStudio, I get an error message: unsupported image format / 32 bit with alpha channel). The .mts file works fine in the streaming player and in the Beta scene builder.

We are aware of the grayscale image problem. There is a similar issue with 3D Photo Studio. The platform simply does not read grayscale images. I'm unsure if this will ever change, so until then I would suggest using desaturated RGB images.