As the title say, I need to combine motion capture data with manual bones rotation in ipi mocap studio, since there's no way in my scene to correctly track forearm rotation. Is It possibile to do this? And how? I tried to copy and paste the forearms poses and then refine the track but it doesn't work: ipi mocap seems to overwrite my poses with its tracking data and not interpolating them with the tracking data.. Anyone knows if this is possible and what's the correct procedure to do this? Thanks!

Mocap Studio doesn't support animation layers if you mean that. However, it is possible to limit tracking to specific body parts keeping others intact.
http://docs.ipisoft.com/Manual_Clean-up#Individual_body_parts_tracking

I've had problems too with forearms, and for me, I'm experimenting with adding another ceiling light to get more light on my arms. But, what's worked for me is using the auto detect actor colors beforehand.