Just an update to my issue, I resolved it by actually using the "Say" parameter and the previous music resumes play. So all is good now.
Example: this is what i use now instead of playing an .mp3 file.
luup.call_action("urn:micasaverde-com:serviceId:Sonos1", "Say",
{Text="The Front door is open", Language="en", GroupZones="ALL",
Volume=40, SameVolumeForAll="true"}, 888)