In this paper, we propose an extended version of sphere decoder (ESD) with the MMSE based enumeration for DL MU-MIMO systems. In previous work, we proposed the ESD which detects interference signals additionally. The ESD can achieve near-optimal performance, but it has much higher complexity than the existing SD. Therefore, this paper presents the improved enumeration based on MMSE. The proposed algorithm can reduce the complexity of ESD significantly while having low performance degradation.