I got the "DSP PLL" one from Amazon. When it works, it does so very well. However, I am trying to use the USB mode where it appears as a sound device to the Raspberry Pi. This seems to work perfectly, as long as you "hotplug" the transmitter to the Pi when the Pi is already booted. If I reboot or power cycle the Pi with the device connected it fails to appear as a sound device to FPP. Confirmed with "lsusb" at the linux command line that the device is missing. If I hotplug the transmitter again, it continues to work perfectly until the next reboot.

The most obvious workaround is just to use a 3.5mm cable to feed the audio to the transmitter and just use the USB for power. But I'm wondering if anyone has figured out how to make the device be detected from a cold boot?