Why the difference between Onkyo HF player and Audirvana?

I'm new to hi rez and have been using the Onkyo HF player running on my iPhone or iPad to play hi rez files for the past 10 months. I've used a few dacs during that time and, most recently, a Benchmark DAC 3.

This morning I downloaded the trial version Audirvana player on my MacBook. I'm considering setting up an older Mac mini as a music server and wanted to check it out.

After listening for the past hour I am shocked at the difference in sound. The differences are not subtle. More detail, way better defined and deeper bass, the soundstage is deeper, and the separation of instruments is better defined.

My question is, why does it sound so much better?

Is the signal the DAC is getting from the MacBook is the same as the signal from the iPhone? The cable is the same. Is the difference the player? Does the MacBook have a higher voltage output than the iPhone? I've played 96, 192, and DSD files and they all sounded better through the MacBook.

I know I've only been listening for an hour but the difference I'm hearing is huge.