Standard adaptation methods are:
More advanced ones
The recent research recommends to consider factored MLLR where specific transforms correspond to speaker, channel and environment
For semi-continuous models only MAP adaptation make sense. If one needs to adapt semi-continuous model with less parameters he need to consider some other methods like this one
CROSSLINGUAL ADAPTATION OF SEMI-CONTINUOUS HMMS USING ACOUSTIC SUB-SIMPLEX PROJECTION Frank Diehl, Asuncion Moreno, Enric Monte
Adaptation is good together with SAT training.
For MAP we can't estimate tau smoothing parameter reliably yet.