If I do that it plays through the internal GM.
Here is the output:
?
? choralis, set: om rotation: 1 path: ? seed: 826083
? choir-satb-layout
make-instrument, name: v1
make-instrument, name: v2
make-instrument, name: v3
make-instrument, name: v4
def-score, name: choralis1
? gen-prob, count: 31 seed: 441896
rnd-sample, size: 31 section: nil exclude: nil seed: 857438
gen-prob, count: 31 seed: 435
gen-choralis
choralis, set: om rotation: nil path: nil seed: 653886
ps
? audition-musicxml-last-score
#<process play loop(10) [Active] #x302002A42ADD>
?
I have preferences / audition set to IAC1.