Ok, I got spamassin to work by telling it to use IPv4 only in the defaults file:
# Duncan Findlay
# WARNING: please read README.spamd before using.
# There may be security risks.
# Change to one to enable spamd
# See man spamd for possible options. The -d option is automatically added.
# SpamAssassin uses a preforking model, so be careful! You need to
# make sure --max-children is not set to anything higher than 5,
# unless you know what you're doing.
OPTIONS="--ipv4-only --create-prefs --max-children 5 --helper-home-dir"
but still have no idea what to do about amavis since it doesn't have this option.