The OP is absolutely correct. He is currently streaming. Streamers are just networking computers made to look like audio components. Audirvana is a program that enhances the computers ability to stream music.
Why get a dedicated streamer? They tend to sound better and not be affected by issues that computers have, such as the need to constantly re update the OS for reasons that are unrelated to playing music. For example I was using an older MacAir with Audirvana for a while, but periodically Apple would force me to do an update that “bricked” my DAC. I would have to call Apple support, they would blame the DAC manufacturer, and a few days later all would be well, but I never had that issue with a dedicated streamer.
If you like the sound of your setup, and you don’t mind having your computer unavailable to you while listening to music, and you aren’t having networking issues, you don’t necessarily need a dedicated streamer.