We experimentally demonstrate the performance of a 10 Gb/s subcarrier multiplexed (SCM) wavelength-division multiplexed (WDM) passive optical network (PON) using 2.5 Gbaud 16-QAM transmission signals. Digital signal processing (DSP) and square-root raised cosine (SRRC) pulse shaping enable both the uplink and downlink channels to achieve net spectral efficiencies up to 2.8 bit/s/Hz per channel using reflective semiconductor optical amplifier (RSOA)-based optical network units (ONUs) and economical 10 GHz intensity modulation and direct detection transceivers. We characterize the system's bit error rate (BER) performance over a 20 km single feeder PON with both remote continuous-wave (CW) seeding and full-duplex transmission scenarios, assuming standard forward error correction (FEC) codes.