Hi Rshad!
Finding a user interface you like is GOLD. Never let it out of your hands. So if you are really happy with the Oppo app and sources, stick with it.
As for looking for a new DAC, USB 2.0 is your ultimate friend. :)
The 105 (unlike the 103) has USB output, giving you great jitter performance with any USB 2.0 capable DAC that is driverless for Mac and Linux. This includes almost all modern DAC's, but some of the earliest models, like the ARC DAC 8 would not work.
Totally worth it. :) The SPDIF connections where more "meh" in my opinion.
It can also output DSD, but I'm not sure about the details. It may only be via HDMI.
Best,
Erik