Anthony,
any domain has the same
dial-string:
<param name="dial-string" value="{presence_id=${dialed_user}@${dialed_domain}}${sofia_contact(${dialed_user}@${dialed_domain})}"/>
and when an extension calls another extension I use:
<action application="bridge" data="{ignore_early_media=true}sofia/$${domain}/${Called_Exten}"/>