Problem with conversion from URDF to SDF

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Hello. Ubuntu 12.04, ROS Hydro, Gazebo 1.9.3

I have successfully ran the rrbot demo in Gazebo; the 3 linkages load, and I can control them from the command line. All very good. Based on that success, I want to extend that to a larger model: 1 World link, 9 joints, 9 links. So, I just add some more links, joints, and transmission elements in hopes that would all work. However, it all goes wrong. If anyone has any insight to this, that would be greatly appreciated -- I've been banging my head against the wall for a couple days on this one.

Issue#1: Gazebo doesn't seem to load to the model.

[ERROR] [1391379571.300875726, 0.023000000]: This robot has a joint named "6dof_joint_1" which is not in the gazebo model.
[FATAL] [1391379571.301168221, 0.023000000]: Could not initialize robot simulation interface

Issue#2: That problem seems to come from the conversion from URDF to SDF, as seen from gzsdf print:

<sdf version='1.4'>
  <model name='6dof'>
    <static>0</static>
    <plugin name='gazebo_ros_control' filename='libgazebo_ros_control.so'>
      <robotNamespace>/6dof</robotNamespace>
    </plugin>
    <link name='__default__'>
      <velocity_decay>
        <linear>0</linear>
        <angular>0</angular>
      </velocity_decay>
    </link>
  </model>
</sdf>

Whereas my URDF model is much larger:

    <?xml version="1.0" ?>
<!-- =================================================================================== -->
<!-- |    This document was autogenerated by xacro from 6dof_arm.xacro                 | -->
<!-- |    EDITING THIS FILE BY HAND IS NOT RECOMMENDED                                 | -->
<!-- =================================================================================== -->
<robot name="6dof" xmlns:xacro="http://ros.org/wiki/xacro">
  <gazebo>
    <plugin filename="libgazebo_ros_control.so" name="gazebo_ros_control">
      <robotNamespace>/6dof</robotNamespace>
    </plugin>
  </gazebo>
  <gazebo reference="6dof_link_base">
    <material>Gazebo/FlatBlack</material>
  </gazebo>
  <gazebo reference="6dof_link_1">
    <material>Gazebo/FlatBlack</material>
    <mu1>0.2</mu1>
    <mu2>0.2</mu2>
  </gazebo>
  <gazebo reference="6dof_link_2">
    <material>Gazebo/FlatBlack</material>
    <mu1>0.2</mu1>
    <mu2>0.2</mu2>
  </gazebo>
  <gazebo reference="6dof_link_3">
    <material>Gazebo/FlatBlack</material>
    <mu1>0.2</mu1>
    <mu2>0.2</mu2>
  </gazebo>
  <gazebo reference="6dof_link_4">
    <material>Gazebo/FlatBlack</material>
    <mu1>0.2</mu1>
    <mu2>0.2</mu2>
  </gazebo>
  <gazebo reference="6dof_link_5">
    <material>Gazebo/FlatBlack</material>
    <mu1>0.2</mu1>
    <mu2>0.2</mu2>
  </gazebo>
  <gazebo reference="6dof_link_hand">
    <material>Gazebo/FlatBlack</material>
    <mu1>0.2</mu1>
    <mu2>0.2</mu2>
  </gazebo>
  <gazebo reference="6dof_link_finger_1">
    <material>Gazebo/FlatBlack</material>
    <mu1>0.2</mu1>
    <mu2>0.2</mu2>
  </gazebo>
  <gazebo reference="6dof_link_finger_2">
    <material>Gazebo/FlatBlack</material>
    <mu1>0.2</mu1>
    <mu2>0.2</mu2>
  </gazebo>
  <material name="carbon_fiber">
    <color rgba="0.792156862745098 0.819607843137255 0.933333333333333 1"/>
  </material>
  <material name="black">
    <color rgba="0.0 0.0 0.0 1.0"/>
  </material>
  <material name="blue">
    <color rgba="0.0 0.0 0.8 1.0"/>
  </material>
  <material name="green">
    <color rgba="0.0 0.8 0.0 1.0"/>
  </material>
  <material name="grey">
    <color rgba="0.2 0.2 0.2 1.0"/>
  </material>
  <material name="orange">
    <color rgba="1.0 0.423529411765 0.0392156862745 1.0"/>
  </material>
  <material name="brown">
    <color rgba="0.870588235294 0.811764705882 0.764705882353 1.0"/>
  </material>
  <material name="red">
    <color rgba="0.8 0.0 0.0 1.0"/>
  </material>
  <material name="white">
    <color ...