Also i had asked if you are using AWG MUx/Demux or conventional MUX/DEMUX in downstream and upstream. you did not mention it.
Anyway, i would still suggest replacing AWG Mux/demux with conventional mux/demux (if so) because i have found performance to improve using conventional mux instead of AWG mux. But i know you will have to configure your design but atleast you can try.Hope it helps.
Regards