Actually my interest is for the (similar) WXC-50, question is: RCA line output is driven/ decoded by the Burr-Brown DAC ?!
Overseas
I do not doubt the correctness of the reply above by Peng, but will add my limited experience and observation using the WXC-50.
First up, as Peng says the signal adjustments seem to be generated on or with the ESS DAC. This suggests that the signals are not adjusted when using the Burr-Brown DAC.
A simple observation of the Yamaha WXC-50 graphical user interface (I mean the web browser settings, not the Android app settings) reveal differences in the features available when throwing the "Mode Switch" on the back of the WXC-50 between the positions "Pre-Amp" and "Player".
Please note that the WXC-50 should be completely turned off from its power source before changing the Mode Switch. Turned Off means there are no LED alight on the front, so the WXC is
unplugged from the wall power supply. It does not mean using the Off button on your Android device which puts the WXC in a powered but standby condition.
So, what do we see?
With the Mode Switch at the back of the WXC in Pre Amp position, using my Android device (phone) app select Settings from the options at the bottom of the screen. On the Settings page look down for ROOM SETTINGS and under there you will see your name for the WXC, click on this. On the next menu look down for EXTERNAL FEATURES and click on Advanced Settings. This will open up your WXC-50 settings in a web browser. On the Advanced Settings menu click on Sound >. This is the revealing part. On the Sound menu the first section will show Pre Amp / Player Mode as PRE AMP and the next section is called Sound (again) which will allow you to set various adjustments to the signal, you will see Enhancer, Bass Extension, Monaural Downmix, and Direct - all with Off / On options with the selection colored blue. Although if Direct is set to On the earlier adjustments are disabled (grayed out).
Now turn off the WXC and unplug it from the power and change the Mode Switch at the back of the WXC to Player position. Find the Sound menu as described above. Now you see all the Sound adjustments mentioned above (including Direct Off/On) are disabled / grayed out.
If you stream music on WXC in the Pre Amp mode you get access to the Yamaha's volume (gain) control on your Android app, but with the Mode Switch set to Player the Yamaha volume/gain control does not exist on the Android app.
The above features suggest to me that with the Mode Switch in Pre Amp position you are using the ESS DAC with DSP (Digital Sound Processing), while in Player mode you are not, that you are using the Burr-Brown DAC.
Tony