Maybe we need to know how you intend to use the DAC; we might start suggesting more expensive solutions than you need.
I gather you are connecting headphones, what model? Are your music sources streaming services such as Spotify, a USB drive or a NAS? Are using the WI-FI option?
Thanks for the replies.
The USB DAC is connected to an amp via a phono cable, so ideally I want line-level out from the DAC as opposed to the headphone-level that my current USB DAC gives. I'm looking for a simple, low cost WiFi based solution. The Pi Xero W handles the streaming from my NAS without bother so that will continue to form the basis of my setup. I like the idea of an I2S add-on to the PiZero so am looking in that direction.
@MarcosCh - You may be able to power the phone and stream from the USB by using an OTG cable? I seem to remember doing something similar when I first had a Chromecast in order to load alternate firmware.