Someone

#plays all 4 and simultaneous sounds with ap aplay esdplay but not play
# kphone1 allows 3; linphone allows 0
pcm.!default {
type  plug;
slave.pcm "dmix"
}

ctl.!default {
type hw
card 0
}

pcm.dsp0 {
type plug
slave.pcm "dmix"
}

ctl.dsp0 {
type hw
card 0
}

ctl.mixer0 {
type hw
card 0
}

pcm.dmixoss {
        type dmix
        ipc_key 321456  # any unique value
        ipc_key_add_uid true
        slave {                 
                pcm "hw:0"
                period_time 0
                period_size 1024  # must be power of 2
                buffer_size 8192  # ditto
        }
}