AtahualpaSeyffert,
I have experienced that problem before, and it is an easy fix. The DTS issue is currently solved, all you need to do to enable it is go to Settings>System>Sound>Device properties>Spatial Sound. Then select DTS Headphone:X in the menu. This is the only way I could get my DTS enabled and stay enabled.
I am sorry that I didn't reply sooner. I encourage you to try this fix and please reply to me if it does or doesn't work.
Have a good day!
Darth Awesome12
Xbox Ambassador