You could use this "trick" to give your adapter a SIP URI that can be directly called. You could then have your ENUM record point to that SIP URI for your adapter.
WARNING:
Most dynamic DNS services only do DNS "A" (normal web) records, whereas some VoIP adapters/equipment REQUIRE DNS "SRV" records instead. So if you are using a dynamic DNS service, you might want to use the "SIP Broker alias" work-around mentioned toward the bottom of that FAQ post (to avoid having people not be able to reach you due to the DNS SRV record issues).
SIP Broker Wiki : Inbound Calls Directly to your LinkSys or Sipura