How to obtain the output from estimated polynomial Model Parameters A B C

I am using the system Identification toolbox and simulink. I am using the ARMAX model structure to obtain an estimate of the output. I am doing online estimation, at some point I want to stop the model identification process and use the estimated A B and C parameters to calculate an output. How do I use these parameters to obtain the output estimated? The ARX to State space conversion block still returns the polynomial modal not state space model that I can use to determine yhat.