Hmmm. Not sure what you mean by the Octo "sensor output". Do you mean the Signal header? If yes, then no I don't think this will work. Cable #53294 is intended to connect the High Flow Next Signal output to the D5 Next Fan/Flow header. I explained the setup procedure to do this in
THIS POST. Did that not work out for you? I don't think the Octo Signal header can output the signal that emulates High Flow #53068 which is the signal that the D5 Next can accept to get High Flow Next flow rate data into it. The Octo Signal header can output a dry contact that can be used to shut down the PC via cable #53216. The Signal output can also output a speed signal but I don't think that signal has anything to do with the High Flow Next. I also don't see the High Flow Next (#53293) listed in the Octo manual section 5.6 list of flow sensors that are compatible with the Octo Flow Sensor input.
If you want to get your High Flow Next flow rate data into the D5 Next, use cable #53294 to connect them as previously explained. I don't understand why you are trying to send the High Flow Next flow rate into the Octo and then send it from there to the D5 Next. Maybe someone from Aquacomputer can chime in here and verify but I don't think what you are trying to do will work.