I'm sure you gurus can make this a lot better, but it's a start. Mostly a butched up hybrid of the 5G iPod and the PSP until it worked. I don't know much about these settings, but every time I tried to deviate from these, things stopped working. I'm not sure what #IPod=yes does, but it's seemingly quite necessary here, as is setting level_idc to 13.
My test conversion was an HD DVR-MS from Vista (x64) Media Center, looked OK, and the audio was in sync during playback.
Hope this helps others.
[WalkmanNWZA720A820]
profile-desc="Sony Walkman NWZ-A720/NWZ-A820"
vf=pullup,softskip,pp=fd,scale=320:-2,crop=320:240,hqdn3d,harddup
lavdopts=threads=2
ovc=x264=yes
x264encopts=threads=auto:subq=5:frameref=4:me=umh:b-pyramid=yes:nocabac=yes:level_idc=13:bitrate=768
oac=faac=yes
faacopts=br=128:raw=yes:mpeg=4:tns=yes:object=2
af=volnorm=1:lavcresample=24000
ofps=30000/1001
of=lavf=yes
lavfopts=format=mp4
#FileExtension=mp4
#IPod=yes