Sorry about the late response. Let’s get through your questions in order:
– Kodi with HDMI audio is no problem with our OS. Kodi comes preinstalled and you can select HDMI for audio in our web interface on in Kodi.
– A SSD might be an issue. We recommend using a powered USB hub to make sure it does not drain the Pi, but it depends on the storage device. Also activate the USB max current option in the Raspberry Settings.
– Squeezebox system is ideal for almost any device, especially iOS and Android (Apps like Squeezer, iPeng, etc. work flawlessly). But you can also just always use the web interface on any device.
– Kodi for music is not ideal, we recommend using the Squeezebox system and its many features and advantages.
– Pi MusicBox, Mopidy, PiCorePlayer, Volumio and Moode are all very different beasts. We cannot speak to their pros and cons. Our OS mostly relies on the Logitech Media Server which is a simple one-click installation and has clean interface and many third party apps and software to control it. The players for it are preinstalled (Squeezelite) on all Max2Play devices so you can easily control the playback of all and synchronize them at will.
– We all use Max2Play here 😛
If you have any more questions, I’d be happy to answer them. But the best way to decide is to just download the free image and try the free main features yourself to see if Max2Play fits your bill 😉