Alternatives to Roon to play SACD-ISO files

????  I don’t know what you mean about "default configuration" but I play the ISOs with the same settings I use for DSF/DFF and they sound the same.

TraX says it does "SACD ISO extraction to many audio formats" but it seems to suggest that it is converting the ISO into another format for storage and playback.  If so, what are you converting them to?

That’s not what I am doing with JRiver.  I am using it to convert the ISO and play it "on-the-fly." I would not recommend JRiver for creating DSD files for storage.

I used Jriver to convert the ISO to DSD to put on my NAS and stream to my DAC. I like having the DSD files. In my testing when I did this using Jriver it sounded really weak compared to the TraX conversion which sounds much better. I thought maybe that’s what you were doing. 

I don't know why your experience with Jriver and direct ISO playback was unsatisfactory to you.  It has not been so for me.  That said, I do not know what you expect to hear, what your system is, what your room is or how you have set up Jriver.  Just relating my experience.

Which version of Jriver were you using?  Until recently, Jriver made such conversions via a PCM intermediary step.