I use my HDP2 when using the V3.
the HDP2 in my experience locks on to whatever digi signal you throw at it w/o complaints but certainly not small
I considered going a raspbery pi solution for small form factor and SPDIF. with a touch display but didnt pursue it. you could probably get an optical connector with a pi as well. Small and most of them run just fine on regular 5vUSB