I just setup AlexaPi for testing with an IQAudio-Digiamp and here is what you might try:
– use Alsa instead Pulseaudio
– try to deactivate all other audioplayers while testing (you might try to use the DMIX audiointerface later to let multiple players connect to the soundcard)
– edit the file „nano /etc/opt/AlexaPi/config.yaml“ and use
output_device: "sysdefault:CARD=sndrpihifiberry" output: "alsa"
– start in Debug mode with „/opt/AlexaPi/src/main.py -d“ to see errors on startup
If you want to use Squeezelite parallel afterwards, you need to setup both Squeezelite and AlexaPi to use the soundcard with DMIX (not tested yet).
Hope this helps.