Make sure obs has desktop audio set to the virtual cable. Obs gets the same exact signal i am hearing in real time, only there is a ghost project running identical along side or behind it with the exception of the added delay and mastering plug-ins. Then I have the second instance of FL 20 running and have that projects audio driver settings set to Focus rite drivers, and I use this for real time nearly no latency in ear monitoring of my mic into my headset and route the audio away from obs and this project does not have the delay plug-in. You can stack these as many as your computer can handle and get delay times of minutes if you wanted to. I then use an audio delay plug-in and set the effect to operare in ms instead of time signatures and then i turn all of the feedback of this audio effect off, so essentially you get the original audio signal without any echoes, only it is delayed to the amount of ms you set the dial to.

One of them is using Image-Lines audio driver settings, with the output set to the virtual cable. What I do is I use FL 20 ( audio software), two of them running at once. I have a 2i2 Scarlett solo 3rd gen sound interface. Hey guys I spent some time with this issue and thankfully found a very simple solution to get the audio delay beyond the 500ms cap inside of OBS.