Try removing the splitter and see if it works. Then in future, do all testing with the splitter removed until you get it working with a direct connection. Only then add the splitter back in.
However, is the source signal protected in some way, such as HDCP? I expect it would be, since AES is being asked for. Plus Roku is unlikely to be allowed to allow HD Digital signals to be output unless the full digital path is HDCP compliant. The symptoms you describe do suggest a deliberate degradation of the signal, consistent with HDCP, although usually you just get nothing through, or on a PC just get told the path isn't compliant.
So, is your full digital path HDCP compliant? That is one reason I suggested removing the splitter for testing. Maybe see if you can find a tool or method to test the digital path is HDCP compliant, or check with Roku/Hauppauge.