Quoted from jabdoa:For sound, we added support for external sound cards in solid state machines (in MPF dev/0.50). This would allow us to implement Spike as an external soundcard as well, put all the sounds on the SD-card and play them on the CPU. However, this interface is very basic and would lack a lot of features such as ducking or crossfade. So while this will work, it would sound worse than our built-in sound system which allows more commercial grade sounds.
I'd personally consider any audio solution that didn't include ducking to be so inferior as to be useless, it's a pretty essential aspect of basic sound design for a pin.