If the priority of the previous PCM launched, is higher than the next PCM, the next PCM will failed.

Test:

On Pulseaudio

1) order:

load-module module-alsa-sink device=Fallback
load-module module-alsa-sink device=Emergency

Result:

Pulse audio OK

2) order:

load-module module-alsa-sink device=Emergency

load-module module-alsa-sink device=Fallback

Result:

Pulse audio KO

ON Alsa:

Run this 2 commands simultaneously, by order:  

1)

speaker-test -DMultimedia -c2 -twav 

speaker-test -DEmergency -c2 -twav

Result: OK

2)

speaker-test -DEmergency-c2 -twav 

speaker-test -DMultimedia -c2 -twav

Result: KO