How to open multiple simultaneous ALSA capture inputs on a single multi-input ALSA card

Question

I am using the ALSA PCM routines to capture audio on an embedded linux system that has a WM8281 audio codec hardware chip which has 6 analog inputs. I have defined several aliases in the /etc/asound.conf file for each of these 6 inputs, each of which has its own settings for rate, channels, format, buffer_size, etc. But all of them are using the same pcm "hw:0,0"

All of this is working great and I can call snd_pcm_open() using any of those aliases defined in the /etc/asound.conf file to open any of the 6 inputs on that codec chip and capture audio successfully.

But I can only open one input at a time. If I try to open a second simultaneous input the snd_pcm_open() for it will fail with a device busy error.

My question is how do I open more than a single capture input?

I am confused about how ALSA uses the term "device". It seems to me that I could define an alias in the /etc/asound.conf file with pcm "hw:0,1" so that the snd_pcm_open() call would use a different device on that card0. But the linux device drivers only initialized a single "device" for capture and playback. My /proc/asound/cards is:

0 [wm82810audio    ]: wm8281_0-audio - wm8281.0-audio

and my /proc/asound/devices is:

2: [ 0- 0]: digital audio playback 3: [ 0- 0]: digital audio capture 4: [ 0]. : control 33: : timer

Is there a way to configure the ALSA drivers to initialize more than one "device" for this card so I could define an alias and use pcm "hw:0,1"? Perhaps in the /etc/modprobe.d/alsa-base.conf file?

I am also confused about how to ALSA uses the term "stream" or "substream". Do I need to define a "stream" or "substream" in the the /etc/asound.conf file? This is an example of how I have currently defined an alias:

  pcm.hs1c-16k {
  type plug
  slave.pcm {
     type dsnoop
     ipc_key 11110002
     slave {
        pcm "hw:0,0"
        rate 16000
        channels 8
        format S16_LE
        buffer_size 640
     }
     bindings [ 0 ] # 0 --> WM8281 IN3R --> AIF1TX1
  }
  hint.description "Headset 1 microphone capture @16k Hz"

}

(The different bindings values will configure a different input on the multi-input codec chip).

Is there a way to define these aliases so I can open multiple independent capture "streams" where each stream captures from a different input on this multi-input codec chip?