Problems with hdaudio(4) on Dell Optiplex-5050

[Brian Buhrow <buhrow%nfbcal.org@localhost>]

	hello.  I'm trying to get the audio headphone jack working properly on
an Dell Optiplex 5050 with NetBSD-9.1 with sources from December 2, 2020.
When sound comes through the built-in speaker, all works fine.  However, if
a stereo headphone is plugged in to the jack on the fron tof the machine,
the audio switches to that jack, but the two channels are mixed together in
such a way as to cause them to cancel each other out on each headphone.  I
think what's going wrong is something like the following:

1.  When the sound card comes up, the speaker is the active device, so both
channels are combined to drive the speaker, monaural mode.  Then, when  a
headphone is plugged in, the sound card is switched to two channels, but
the two channels are still mixed.  From what I gather reading the source,
the initial set up is how the BIOS  sets things up, so the driver just
leaves things as they are and switches the output from speaker to headphone
when the headphone is connected.  I've seen reports of similar problems
with the NetBSD driver and other Dell models, so I'm confident it's a
software problem.  I looked at the FreeBSD-12 driver to see what they do,
and it appears they attach all the jacks as  different devices, but they
also don't seem to switch modes, so their driver might have the same issue.
	Does anyone have any ideas what I should look at to resolve this
issue?
-thanks
-Brian

NetBSD 9.1_STABLE (GENERIC) #0: Mon Dec  7 14:11:20 PST 2020
	buhrow%loth-9.nfbcal.org@localhost:/usr/local/netbsd/src-90/sys/arch/amd64/compile/GENERIC

 . . .

hdaudio0 at pci0 dev 31 function 3: HD Audio Controller
hdaudio0: interrupting at msi2 vec 0
hdafg0 at hdaudio0: vendor 10ec product 0255
hdafg0: DAC00 2ch: Speaker [Jack]
hdafg0: 2ch/0ch 44100Hz 48000Hz 96000Hz 192000Hz PCM16 PCM20 PCM24 AC3
audio0 at hdafg0: playback, capture, full duplex, independent
audio0: slinear_le:16 2ch 48000Hz, blk 1920 bytes (10ms) for playback
audio0: slinear_le:16 2ch 48000Hz, blk 1920 bytes (10ms) for recording
spkr0 at audio0: PC Speaker (synthesized)
wsbell at spkr0 not configured
hdafg1 at hdaudio0: vendor 8086 product 2809
hdafg1: DP00 8ch: Digital Out [Jack]
hdafg1: 8ch/0ch 48000Hz PCM16*

-thanks
-Brian