I did a test with the newest image on my opi-one-plus, and still have the same problem (black screen). I tested multiple cables on my TV and monitor (all are working fine with various pis, odroids etc.), and I finally had a signal on the monitor (but not stable). Funny thing is: my TV has multiple inputs and it switches to the input the opi is connected to, so there must be at least a weak signal.
My question is: can you make the HDMI-signal stronger? Since the desktop image of Xulong is working fine, I assume they use a stronger HDMI-signal.