It occurred to me that Thierry Lacoste wrote in gmane.os.netbsd.help:
> $ timidity ipanema.mid
> /dev/sound: Device busy
> Couldn't open NetBSD audio device (`d')
>
> I guess this is because KDE opens /dev/sound
> because timidity works fine with twm.
>
> Any tips?

Other than the obvious: No.

The obvious being:

1) Try whether timidity works using artsdsp (artsdsp timidity ipanema.mid).
   Not a really big chance it will, though.
1a) Have timidity use stdout for sound output (-Or? It's been a while), 
   and pipe that through artscat
2) Keep an artscontrol panel open - you can suspend the arts sound daemon
   there, which will release the sounddevice
3) Disable a lot of the KDE sounds, so artsd gets to sleep moreoften and
   longer
4) Lower the default timeout (30 seconds) before artsd goes to sleep (see
   the control center for that)

FreeBSD has vchans for this, but sadly, we don't :(