I have a multi-channel card that is detected as:
> Mar 18 08:08:56 yv kernel: hdacc0: <NVIDIA (0x001c) HDA CODEC> at cad 0 on hdac0
> Mar 18 08:08:56 yv kernel: hdaa0: <NVIDIA (0x001c) Audio Function Group> at nid 1 on hdacc0
> Mar 18 08:08:56 yv kernel: pcm0: <NVIDIA (0x001c) (HDMI/DP 8ch)> at nid 4 on hdaa0
> Mar 18 08:08:56 yv kernel: pcm1: <NVIDIA (0x001c) (HDMI/DP 8ch)> at nid 5 on hdaa0
> Mar 18 08:08:56 yv kernel: hdacc1: <Realtek ALC889 HDA CODEC> at cad 0 on hdac1
> Mar 18 08:08:56 yv kernel: hdaa1: <Realtek ALC889 Audio Function Group> at nid 1 on hdacc1
> Mar 18 08:08:56 yv kernel: pcm2: <Realtek ALC889 (Rear Analog 7.1/2.0)> at nid 20,22,21,23 and 24,26 on hdaa1
> Mar 18 08:08:56 yv kernel: pcm3: <Realtek ALC889 (Front Analog)> at nid 27 and 25 on hdaa1
> Mar 18 08:08:56 yv kernel: pcm4: <Realtek ALC889 (Onboard Digital)> at nid 30 on hdaa1
> Mar 18 08:08:56 yv kernel: pcm5: <Realtek ALC889 (Rear Digital)> at nid 17 on hdaa1

Sound Mixer picks only one element as a choice: Realtek ALC889 (Rear Analog 7.1/2.0)

I use more than one channel. xfce4 doesn't allow this:
1. It needs to allow multiple instances.
2. It needs to allow to choose other channels.

xfce4-mixer-4.11.0_3 on FreeBSD.