Right, I've been puzzling over this problem for the past month, as I tried to get Raspyfi to recognise my rPAC correctly. Like you, if the device was connected at boot up, nothing would play – Raspyfi was frozen. If I connected the device after boot it simply wasn't recognised by alsamixer (F6 / output device etc).
I now know why. By default the rPAC is a USB audio 1 device – this is make it a Plug & Play device in Windows – no driver required. Hence the 96/24 limitation. However the rPAC can be forced to boot as a USB audio 2 device. Simply hold down the volume up & down buttons as you plug in the USB plug to the RPi (in my case into a powered USB hub connected to the Pi). Then power up the Pi. Start playing something from the playlist. At first you'll hear nothing – just press volume up button on the rPAC and behold…………..! So far I've been listening to 96/24 files – will download some 192/24 & test those this afternoon.
Hope this resolves your problems. Enjoy!