Still having this problem with lucid and my USB DAC.  Here's a more minimal set of messages.  The underruns occurred about 5 minutes into playing the first song of the day with Rhythmbox.  The audio effect was a sort of "stutter" in the music.

I would be pleased to run apport or any other testing required!

May  8 09:26:42 temuko pulseaudio[1309]: alsa-sink.c: Trying resume...
May  8 09:26:42 temuko pulseaudio[1309]: alsa-sink.c: Resumed successfully...
May  8 09:26:42 temuko pulseaudio[1309]: alsa-sink.c: Starting playback.
May  8 09:26:42 temuko pulseaudio[1309]: ratelimit.c: 1 events suppressed
May  8 09:26:42 temuko pulseaudio[1309]: sink-input.c: Created input 1 "Playback Stream" on alsa_output.usb-Burr-Brown_from_TI_USB_Audio_CODEC-00-default.analog-stereo with sample spec s16le 2ch 44100Hz and channel map front-left,front-right
May  8 09:26:42 temuko pulseaudio[1309]: sink-input.c:     media.name = "Playback Stream"
May  8 09:26:42 temuko pulseaudio[1309]: sink-input.c:     application.name = "Rhythmbox"
May  8 09:26:42 temuko pulseaudio[1309]: sink-input.c:     native-protocol.peer = "UNIX socket client"
May  8 09:26:42 temuko pulseaudio[1309]: sink-input.c:     native-protocol.version = "16"
May  8 09:26:42 temuko pulseaudio[1309]: sink-input.c:     media.role = "music"
May  8 09:26:42 temuko pulseaudio[1309]: sink-input.c:     application.process.id = "2016"
May  8 09:26:42 temuko pulseaudio[1309]: sink-input.c:     application.process.user = "clh"
May  8 09:26:42 temuko pulseaudio[1309]: sink-input.c:     application.process.host = "temuko"
May  8 09:26:42 temuko pulseaudio[1309]: sink-input.c:     application.process.binary = "rhythmbox"
May  8 09:26:42 temuko pulseaudio[1309]: sink-input.c:     application.icon_name = "rhythmbox"
May  8 09:26:42 temuko pulseaudio[1309]: sink-input.c:     window.x11.display = ":0.0"
May  8 09:26:42 temuko pulseaudio[1309]: sink-input.c:     application.language = "en_CA.utf8"
May  8 09:26:42 temuko pulseaudio[1309]: sink-input.c:     application.process.machine_id = "76ff65a789ddffd68a9d1bfd4bdb541e"
May  8 09:26:42 temuko pulseaudio[1309]: sink-input.c:     application.process.session_id = "76ff65a789ddffd68a9d1bfd4bdb541e-1273334136.700155-1606288336"
May  8 09:26:42 temuko pulseaudio[1309]: sink-input.c:     module-stream-restore.id = "sink-input-by-media-role:music"
May  8 09:26:42 temuko pulseaudio[1309]: protocol-native.c: Requested tlength=200.00 ms, minreq=10.00 ms
May  8 09:26:42 temuko pulseaudio[1309]: protocol-native.c: Final latency 200.00 ms = 90.00 ms + 2*10.00 ms + 90.00 ms
May  8 09:30:28 temuko pulseaudio[1309]: alsa-sink.c: Underrun!
May  8 09:30:28 temuko pulseaudio[1309]: alsa-sink.c: Increasing wakeup watermark to 30.00 ms
May  8 09:30:40 temuko pulseaudio[1309]: ratelimit.c: 7 events suppressed
May  8 09:30:40 temuko pulseaudio[1309]: alsa-sink.c: Underrun!
May  8 09:30:40 temuko pulseaudio[1309]: alsa-sink.c: Increasing wakeup watermark to 40.00 ms
May  8 09:30:42 temuko pulseaudio[1309]: module-suspend-on-idle.c: Sink alsa_output.usb-Burr-Brown_from_TI_USB_Audio_CODEC-00-default.analog-stereo idle for too long, suspending ...
May  8 09:30:42 temuko pulseaudio[1309]: alsa-sink.c: Device suspended...