In this paper we present the table-based tangible interface application Xenakis which uses probability models in order to compose music in a way that can be strongly influenced by the user. Our musical sequencing application is based on a framework for tangible interfaces with an architecture that is strongly inspired by the model-view-controller pattern. In addition, we developed a hardware setup for tangible interfaces and used MatraX for tracking markers. The sequencer is the first implementation based on this framework. It allows users to create music simply by moving tangibles on the table. The graphics engine Horde3D is used to visualize the user-interaction and to show the relationships between the tangible objects on the table, creating an appealing audio-visual experience. An evaluation with 37 first time users was conducted in order to discover the strong and the weak points of such tangible user interfaces, especially in the context of our application.