As a follow-up, yesterday evening I had my XLO burn-in track on repeat and the DS was playing it over and over like it should. I went out to dinner and when I came back home I found that the DS USB display was “red." The DS somehow lost the signal from my MacMini and it was no longer getting my XLO burn-in track despite my MacMini still showing it as playing. I then changed inputs on my DS remote quickly from USB to another input, I2S I believe, and then back to USB. After doing that the USB light then changed from “red” to “green” and the music suddenly started playing again.
As an experiment, last night I disconnected my USB cable from the DS and left the DS on all night. Even though the USB cable was disconnected, the USB display light remained green all night. It shouldn’t do that, right?
This morning I reconnected the USB cable to the DS, turned on my MacMini, preamp, and amp and then cued up an album from my iPad. Without having to reboot the DS, the music started playing immediately. This is the second time that the DS played music without me having to reboot it and change settings in my System Preference and Midi. However there seems to be no consistency in whether the DS can play music without rebooting from the rear panel off/on switch.
I hope that this follow up info helps in solving my problem.