Hi Avrom,
Firstly, have you seen the iPeng application that uses the Squeezebox emulation to make an iPad a Roon endpoint ? It is limited to resolutions supported by Squeezebox, rather than a RAAT capable endpoint which is limited by hardware. It is also groupable only with other Squeezebox zones and not RAAT zones. Nevertheless it provides a very clean signal to the iPad which is then subject to the internal DAC etc. It is by far the best sound to come out of the internal speakers of my iPad (haven’t tried headphones yet).
If you have seen the iPeng app and it doesn’t suit your requirements then let’s ask @Rugby what Android options he thinks might suit and invite discussion from anyone else as to suggested hi quality Control/Output devices.