You want to build a local transformation matrix for each joint. As you stated, the component transforms are in SRT order (for post multiplication). For clarify, that means you first apply the scaling matrix, then the rotation matrices, then the translation matrix. You can treat each Euler rotation as a separate matrix, with the result being (S * Rz * Ry * Rx * T). The order of multiplication is actually defined by the Collada file (you'll notice that the order is Rotate Z/Y/X).
Finally, in Collada, the skeletons can be instanced, which is where the offset matrix comes into play. In short, you have to apply the offset matrix to the root of the joint skeleton.