sndio play multiple wav files ?

Hi!,

I am working on a curses C sndio app to
play samples that are just wav files.
I would like to be able to play them
"over each other" like not sequentially.

(I would like for the wav file to play
regardless if another one is already playing.)

I can play ONE wav file using sndio.

https://codeberg.org/pkw/siotest/src/branch/main/siotest.c#L130

What is the easiest and most idiomatic way
to play multiples ones ?

My naive approach is to just do the same thing
as I would do for one and put that into
a pthread.  That means I am opening the 
sndio device each time.  (sio_open)

I see in game programming people do "mixing"
of sound. 

Any pointers or places to look?
I want to use just OpenBSD and sndio if possible.
I am using libsndfile, but that is just to
open the wav files easily.

thanks!
--
Paul W