Today game engines deal with not only game contents or assets, but also gain the ability to play music. We will soon see that the DAW (digital audio workstation) and the game engine will be merged into a more general and sophisticated musical environment. The authors are developing a prototype ensemble system in which several client PCs are managed with a REST http server. Each client plays its cello, piano, or some synthesizer part conducted by the server. The clients also send control signals to others to change the tempo, rhythm or pitch improvisationally.  Experimental results show that the Modular Synth component in the Unreal Engine 4 can play pieces of chamber music composed by the authors almost synchronously via LAN.