Physical (or physics-based) modeling of musical instruments is one of the main research fields in computer music. A basic question, with increasing research interest recently, is to understand how different discrete-time modeling paradigms are interrelated and can be combined, whereby wave modeling with wave quantities (W-methods) and Kirchhoff quantities (K-methods) can be understood in the same theoretical framework. This paper presents recent results from the HUT Sound Source Modeling group, both in the form of theoretical discussions and by examples of Kvs. W-modeling in sound synthesis of musical instruments.