To follow up and for whoever it might help :
THe Koss ProDJ100 works beautifully well with the O2 amp and HiFiMeDIY Sabre Dac. Its a superb system and matches up great. Much better soundstage with the DAC, which is remarkable for 40$. I wouldn't recommend the DAC alone, as it sounds much better on low volume, the O2 complements that part. Now for M50 replacement pads!