Animation rigging with muscle humanoid settings?

Hello, I'm trying to setup an idle character whom arms and head can be moved by the player in VR.

In order to do this, I've setup an animation rig with an aim (head) and a 2 bones IK (arms) constraints. This is working perfectly fine and the arms and head are moving accordingly. (Using 2019.4)

My problem is, the constraints are overriding the muscle settings for the humanoid rig. The source objects which control the arms and head can be moved anywhere in the world space and the character could be placed in a non natural position (like having his head tilted at 180°).

The limits provided by the rig constraints are too simple, and force manually the source object in the space seems difficult to me in order to achieve a reallistic behavior (in case of the arm movement for example).

Is there a way to use the animation rigging while keeping the behavior of the muscle setting from the humanoid rig?

KR,
Raphaël