Poor sound with Dell onboard Conexant CX20641 / HDA intel soundcard

Some Dell machines have a soundcard that is essentially wired up differently to how some software expects. This can be evident when using the line-out of the machine to go into speakers and finding that there is very poor bass output but can manifest itself in other soundcard jacks not behaving as expected. This is observed during enforced homeschooling on an old Dell Optiplex 390 running Fedora 32.

Verifying the soundcard is using a similar troublesome chipset:

$ dmesg | grep snd_hda_codec_conexant [ 19.026492] snd_hda_codec_conexant hdaudioC0D2: CX20641: BIOS auto-probing. $ lspci -v -d 8086:1c20 00:1b.0 Audio device: Intel Corporation 6 Series/C200 Series Chipset Family High Definition Audio Controller (rev 04) DeviceName: Onboard Audio Subsystem: Dell Device 04f5 Flags: bus master, fast devsel, latency 0, IRQ 36 Memory at e4c30000 (64-bit, non-prefetchable) [size=16K] Capabilities: Kernel driver in use: snd_hda_intel Kernel modules: snd_hda_intel