The system identification tool is capable of parametric, polynomial, frequency-based, and grey box algorithms. You shouldn't be limited to only linear methods. If you're looking for examples on how to use this toolkit, there's a number of examples that can be found in the NI Example Finder. In LabVIEW, Go to Help >> Find Examples. When that box pops up, browse to Toolkits and Modules >> System Identification. There should be a number of examples to be found here. I hope this helps!
