Can you elaborate when you say “this does not account for the RTL”? The audio is being sent from the DAW out of the interface, through the H9000, and back to the DAW via the interface. What additional latency is there? If you are using the Pipeline plug-in, all of this latency should be accounted for when you ping the FX Chain.
I don’t have Studio One to test this, but I just set up a similar test using Logic’s Audio I/O plug-in and the latency compensation seems to be working correctly. I can ping the plug-in and it will report various sample latency’s depending on my algorithm configurations. Once the latency is configured, the audio will sound correctly compensated. If I am using a reverb plug-in that has pre-delay, the pre-delay will introduce an additional delay before the sound is processed by the reverb.
It sounds like perhaps the Pipeline delay compensation isn’t working correctly.