As Fiber-to-the-Room (FTTR) networks proliferate, multi-device deployments pose significant energy consumption challenges. This paper proposes a Quality of Service (QoS)-aware energy-saving scheme based on a multi-threshold buffer energy saving (MBES) scheme to reduce consumption while ensuring energy QoS. MBES leverages the centralized control of the main fiber unit (MFU) and the wireless-state awareness of subordinate fiber units (SFUs) for synergistic fiber-wireless energy savings. The scheme assigns independent, dynamic buffer thresholds to service queues on SFUs, enabling low-latency reporting for high-priority traffic while accumulating low-priority data to extend sleep cycles. At the MFU, a coordinated scheduling algorithm accounts for Wi-Fi access delay and creates an adaptive closed-loop control by adjusting SFUs’ buffer thresholds based on end-to-end delay feedback. Simulation results show that, while satisfying strict latency requirements, MBES achieves a maximum energy saving of 17.75% compared with the no energy saving (NES) scheme and provides a superior trade-off between latency control and energy efficiency compared with the single-threshold buffer energy saving (SBES) scheme.