The full and seamless integration of wireless devices with traditional fixed networks is more and more important to foster the mobile and ubiquitous access to the Internet. In particular, the heterogeneity and resource limitations of wireless devices motivate novel support infrastructures that can facilitate the wired-wireless integration and can provide service tailoring depending on client characteristics. The paper presents an application-level portable middleware, called ubiQoS, for QoS-enabled audio streaming to Bluetooth clients. ubiQoS exploits support proxies for QoS tailoring and for managing the QoS over the last segment of the audio distribution path towards the clients, by using different types of Bluetooth links. Proxies execute at the wired-wireless network edges and can even migrate to follow the device movements, where and when needed. The reported experimental results show the feasibility of the application-level approach in the challenging case of QoS-enabled audio streaming to resource-limited Bluetooth devices.