I've three three sinks, everyone is functional:

Ziel #0
        Status: SUSPENDED
        Name: alsa_output.pci-0000_00_1b.0.analog-surround-51
        Beschreibung: Internes Audio Analog Surround 5.1
        Treiber: module-alsa-card.c
        Abtastwert-Angabe: s16le 6ch 96000Hz
        Kanalzuordnung: front-left,front-right,rear-left,rear-right,front-center,lfe
        Besitzer-Modul: 7
        Stumm: nein
        Lautstärke: front-left: 65536 / 100% / 0,00 dB,   front-right: 65536 / 100% / 0,00 dB,   rear-left: 65536 / 100% / 0,00 dB,   rear-right: 65536 / 100% / 0,00 dB,   front-center: 65536 / 100% / 0,00 dB,   lfe: 65536 / 100% / 0,00 dB
                Verteilung 0,00
        Basis-Lautstärke: 65536 / 100% / 0,00 dB
        Quellen-Monitor: alsa_output.pci-0000_00_1b.0.analog-surround-51.monitor
        Latenz: 0 usec, eingestellt 0 usec
        Flags: HARDWARE HW_MUTE_CTRL HW_VOLUME_CTRL DECIBEL_VOLUME LATENCY 
        Eigenschaften:
                alsa.resolution_bits = "16"
                device.api = "alsa"
                device.class = "sound"
                alsa.class = "generic"
                alsa.subclass = "generic-mix"
                alsa.name = "ALC1150 Analog"
                alsa.id = "ALC1150 Analog"
                alsa.subdevice = "0"
                alsa.subdevice_name = "subdevice #0"
                alsa.device = "0"
                alsa.card = "0"
                alsa.card_name = "HDA Intel PCH"
                alsa.long_card_name = "HDA Intel PCH at 0xef830000 irq 67"
                alsa.driver_name = "snd_hda_intel"
                device.bus_path = "pci-0000:00:1b.0"
                sysfs.path = "/devices/pci0000:00/0000:00:1b.0/sound/card0"
                device.bus = "pci"
                device.vendor.id = "8086"
                device.vendor.name = "Intel Corporation"
                device.product.id = "8ca0"
                device.product.name = "9 Series Chipset Family HD Audio Controller"
                device.form_factor = "internal"
                device.string = "surround51:0"
                device.buffering.buffer_size = "115200"
                device.buffering.fragment_size = "28800"
                device.access_mode = "mmap"
                device.profile.name = "analog-surround-51"
                device.profile.description = "Analog Surround 5.1"
                device.description = "Internes Audio Analog Surround 5.1"
                module-udev-detect.discovered = "1"
                device.icon_name = "audio-card-pci"
        Ports:
                analog-output-lineout: Line Out (Typ: Line, Priorität: 9000, verfügbar)
        Aktiver Port: analog-output-lineout
        Formate:
                pcm

Ziel #1
        Status: SUSPENDED
        Name: alsa_output.usb-Native_Instruments_Komplete_Audio_6_679246F4-00.analog-stereo-out-ab
        Beschreibung: Komplete Audio 6 Analog Stereo 1/2
        Treiber: module-alsa-card.c
        Abtastwert-Angabe: s32le 6ch 96000Hz
        Kanalzuordnung: front-left,front-right,aux0,aux1,aux2,aux3
        Besitzer-Modul: 8
        Stumm: nein
        Lautstärke: front-left: 53649 /  82% / -5,22 dB,   front-right: 53649 /  82% / -5,22 dB,   aux0: 53649 /  82% / -5,22 dB,   aux1: 53649 /  82% / -5,22 dB,   aux2: 53649 /  82% / -5,22 dB,   aux3: 53649 /  82% / -5,22 dB
                Verteilung 0,00
        Basis-Lautstärke: 65536 / 100% / 0,00 dB
        Quellen-Monitor: alsa_output.usb-Native_Instruments_Komplete_Audio_6_679246F4-00.analog-stereo-out-ab.monitor
        Latenz: 0 usec, eingestellt 0 usec
        Flags: HARDWARE DECIBEL_VOLUME LATENCY 
        Eigenschaften:
                alsa.resolution_bits = "32"
                device.api = "alsa"
                device.class = "sound"
                alsa.class = "generic"
                alsa.subclass = "generic-mix"
                alsa.name = "USB Audio"
                alsa.id = "USB Audio"
                alsa.subdevice = "0"
                alsa.subdevice_name = "subdevice #0"
                alsa.device = "0"
                alsa.card = "2"
                alsa.card_name = "Komplete Audio 6"
                alsa.long_card_name = "Native Instruments Komplete Audio 6 at usb-0000:0c:00.0-1, high speed"
                alsa.driver_name = "snd_usb_audio"
                device.bus_path = "pci-0000:0c:00.0-usb-0:1:1.0"
                sysfs.path = "/devices/pci0000:00/0000:00:1c.6/0000:0c:00.0/usb5/5-1/5-1:1.0/sound/card2"
                udev.id = "usb-Native_Instruments_Komplete_Audio_6_679246F4-00"
                device.bus = "usb"
                device.vendor.id = "17cc"
                device.vendor.name = "Native Instruments"
                device.product.id = "1001"
                device.product.name = "Komplete Audio 6"
                device.serial = "Native_Instruments_Komplete_Audio_6_679246F4"
                device.string = "hw:2,0,0"
                device.buffering.buffer_size = "230400"
                device.buffering.fragment_size = "57600"
                device.access_mode = "mmap"
                device.profile.name = "analog-stereo-out-ab"
                device.profile.description = "Analog Stereo 1/2"
                device.description = "Komplete Audio 6 Analog Stereo 1/2"
                module-udev-detect.discovered = "1"
                device.icon_name = "audio-card-usb"
        Formate:
                pcm

Ziel #2
        Status: SUSPENDED
        Name: jack_out
        Beschreibung: JACK sink (PulseAudio JACK Sink)
        Treiber: module-jack-sink.c
        Abtastwert-Angabe: float32le 2ch 88200Hz
        Kanalzuordnung: front-left,front-right
        Besitzer-Modul: 11
        Stumm: nein
        Lautstärke: front-left: 65536 / 100% / 0,00 dB,   front-right: 65536 / 100% / 0,00 dB
                Verteilung 0,00
        Basis-Lautstärke: 65536 / 100% / 0,00 dB
        Quellen-Monitor: jack_out.monitor
        Latenz: 0 usec, eingestellt 0 usec
        Flags: DECIBEL_VOLUME LATENCY 
        Eigenschaften:
                device.api = "jack"
                device.description = "JACK sink (PulseAudio JACK Sink)"
                jack.client_name = "PulseAudio JACK Sink"
                device.icon_name = "audio-card"
        Formate:
                pcm

plasma-pa show me only the first two sinks, the third – jack_out – not. I can't also move playing applications like firefox to the jack sink.

SOFTWARE/OS VERSIONS
Linux: Gentoo Linux 2.8
KDE Plasma Version: 5.25.2
KDE Frameworks Version: 5.95.0
Qt Version: 5.15.5