I talked to, I believe, Malcolm about 6 months ago. He said he added mlookatup expression, which is awesome, but I looking to solve for a rotation order.
There currently isn’t an explodematrix expression, I’ll look into adding it.
Only thing I can think of right now is: If you can get your 16 values from the matrix into a CHOP (1 value per channel). You can then assign the CHOP as the transform matrix in an Object on the Pre-Transform page (CHOP Matrix is the parameter name). Then you can use the Object CHOP to get the RX, RY RZ of that Object.
Roundabout way but right now thats the only way I think.