Further information. Minecraft runs fine with sound turned off. If sound is turned on and I run jstack on the Minecraft process, it shows the main thread blocks in sound-related code.
"Minecraft main thread" daemon prio=6 tid=0000000003008000 nid=0xb20be000 waiting for monitor entry [00000000b20bd000]
java.lang.Thread.State: BLOCKED (on object monitor)
at paulscode.sound.SoundSystem.CommandQueue(SourceFile:2361)
waiting to lock <000000000924bd48> (a java.lang.Object)
at paulscode.sound.SoundSystem.setVolume(SourceFile:978)
at bcx.a(SourceFile:78)
at ard.a(SourceFile:206)
at atc.b(SourceFile:32)
at arl.a(SourceFile:50)
at asw.a(SourceFile:27)
at aso.a(SourceFile:98)
at ayt.b(SourceFile:755)
at net.minecraft.client.Minecraft.J(SourceFile:604)
at net.minecraft.client.Minecraft.run(SourceFile:534)
at java.lang.Thread.run(Thread.java:680)
This is an Intel Mac, but I'll try an older CodecJOrbis and report back.