Use jackd with a NVidia HDMI audio interface

My PulseAudio server, connected to "GF119 HDMI Audio Controller", outputs audio fine for my HDMI monitor. Google seems to indicate this is provided by the NVidia card. However, when I try to start jackd over hw:1,3 or hw:1,7 (which aplay -l tells me is the NVidia card), the command outputs the following:

$ jackd -R -d alsa -d hw:1,3
jackdmp 1.9.12
Copyright 2001-2005 Paul Davis and others.
Copyright 2004-2016 Grame.
Copyright 2016-2017 Filipe Coelho.
jackdmp comes with ABSOLUTELY NO WARRANTY
This is free software, and you are welcome to redistribute it
under certain conditions; see the file COPYING for details
no message buffer overruns
no message buffer overruns
no message buffer overruns
JACK server starting in realtime mode with priority 10
self-connect-mode is "Don't restrict self connect requests"
audio_reservation_init
Acquire audio card Audio1
creating alsa driver ... hw:1,3|hw:1,3|1024|2|48000|0|0|nomon|swmeter|-|32bit
ALSA: Cannot open PCM device alsa_pcm for capture. Falling back to playback-only mode
configuring for 48000Hz, period = 1024 frames (21.3 ms), buffer = 2 periods
ALSA: final selected sample format for playback: 32bit integer little-endian
ALSA: use 2 periods for playback

However, when I try to play sound via Ardour or JackKeyboard, it outputs no sound. This also happens for hw:1,7.

The output of aplay -l is as follows:

$ aplay -l
**** List of PLAYBACK Hardware Devices ****
card 0: MID [HDA Intel MID], device 0: ALC887 Analog [ALC887 Analog] Subdevices: 1/1 Subdevice #0: subdevice #0
card 0: MID [HDA Intel MID], device 1: ALC887 Digital [ALC887 Digital] Subdevices: 1/1 Subdevice #0: subdevice #0
card 1: NVidia [HDA NVidia], device 3: HDMI 0 [HDMI 0] Subdevices: 1/1 Subdevice #0: subdevice #0
card 1: NVidia [HDA NVidia], device 7: HDMI 1 [HDMI 1] Subdevices: 1/1 Subdevice #0: subdevice #0

Using the hw:0 devices does not work either. I have tried using QJackCtl with an increased buffer size, but to no avail. I've also tried turning pulseaudio's output devices to "Off" and retrying the configuration. I do not know how else to troubleshoot this. I am using Ubuntu Studio 20.04. What does "playback-only" mode mean, and is it the reason why it's not outputting audio? I am using Jack 1.9.12.

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