Is alpha map compression possible in Stream Tuning Studio?

No- well, at least not technically. While Stream Tuning Studio supports alpha maps, it does not compress them as separate textures. Thus they are treated as part of the associated diffuse texture.

~Chris

Chris is right that lighmaps are not separable from textures in Stream Tuning Studio. To be exact, you can set the compression ratio for alpha channels - it will just coincide with the compression ratio for the rest of the texture. If you do 50% TrixelsNT for the texture then the lightmap will have the same comression.

Michael