asound.conf

pcm.!default {
	type plug
	playback.pcm "out"
	capture.pcm "loopin"
}
pcm.out {
    type plug
    slave.pcm {
        type multi
        slaves {
            a { channels 2 pcm "output" }
            b { channels 2 pcm "loopout" }
        }
        bindings {
            0 { slave a channel 0 }
            1 { slave a channel 1 }
            2 { slave b channel 0 }
            3 { slave b channel 1 }
        }
    }
    ttable [
        [ 1 0 1 0 ]   # left  -> a.left,  b.left
        [ 0 1 0 1 ]   # right -> a.right, b.right
    ]
}

pcm.loopout {
    type dmix
	ipc_key 1025
	slave.pcm "hw:3,0,0"
    slave {
        period_time 0
        period_size 1024
        buffer_size 8192
        channels 2
    }
    bindings {
        0 0
        1 1
    }
}

pcm.loopin {
    type plug
	slave.pcm "hw:3,1,0"
}

pcm.output {
	type dmix
	ipc_key 1024
	slave.pcm "hw:1,0"
    slave {
        period_time 0
        period_size 1024
        buffer_size 8192
        channels 2
    }
    bindings {
        0 0
        1 1
    }
}