From my build thread...post #148:
https://www.xbimmers.com/forums/show...2#post26228982
UPDATE 5/28 - Audio Switching - Minor progress. Right now I have the Y Splitter in the OEM AUX IN, and the USB/DAC and Android AUX OUT connected to the Y Splitter. Some research allowed me to determine that Android Developer Mode has an audio switching function called 'seamless transfer' which could allow the unit to switch between audio sources (USB and AUX OUT). 4x4 Shop does not recommend activating developer. Before attempting that path, I did find an app called Lesser AudioSwitch and decided to try that first. After setting it up
I now have sound from non-USB functions including CARPLAY, however it is very low/faint and hissy. Increasing the OEM Aux Volume from 5 to max increases the poor sound a little bit, but when I play UAPP it clips. I could adjust volume limits and gain within UAPP, but that won't change the poor Aux Output sound I'm hearing. So reduced the Aux Volume back down to 5. I noticed the USB audio wasn't sounding exceptional. I removed my USB extension and sound improved. I swapped out the audioquest big sur aux cable for the old SIIG I used in my Avin unit and the sound became very bright, tangibly different, which was surprising to me for just swapping aux cables. Of course one was $115 and the other $20. With the AUX OUT plugged in directly to the AUX IN (using a Monster Aux Cable ~$35), the sound is pretty good as I've noted before. SO why would it suddenly decrease drastically through the Aux Y Splitter? I'm using a Y splitter that is <$10 b/c I could get it fast and I didn't want to spend a lot for something that might not work...I think I will upgrade...Quick note on the switching app...it worked pretty good and I could switch between audio pretty smoothly...it does STOP my music though and I have to press play to continue when switching back to music...also there was a notice that when the device is rebooted, the settings are reset :-/...one problem at a time, lol.
UPDATE: It's not the Aux Y-Splitter...at least it doesn't appear so...I remove the usb/dac line from the Y-Splitter and the AUX out sound is fine.
UPDATE 5/30 -
SOLVED! but work still remains - It's not the cheap Aux Y Splitter. I removed the dragonfly DAC and dropped in my OPPO H2A-SE DAC and it works! I know have both sources able to play at the sound qualities described in my build thread. They are switched via Android using the Lesser AudioSwitch App. However the OPPO is not ideal for this application, it is my all-in-one (phone charger, headphone amp, dac) when I go on travel. I need to find a new inline DAC that's compatible with my UAPP app...going through their list of applicable DACs.