the modules node should not be a child of the firmware node, but rather directly of airframe.
<airframe name="BenchTest">
<firmware name="fixedwing">
<target name="sim" board="pc">
<!--define name="USE_MAGNETOMETER" value="TRUE"/-->
<subsystem name="radio_control" type="ppm"/>
</target>
<target name="ap" board="lisa_m_2.0">
<!--define name="LISA_M_LONGITUDINAL_X"/-->
<define name="AGR_CLIMB"/>
<define name="USE_I2C1"/>
<!--define name="USE_AIRSPEED"/-->
<define name="RADIO_EXPO" value="RADIO_GEAR"/>
<subsystem name="radio_control" type="spektrum">
<!--define name="RADIO_MODE" value="RADIO_AUX1"/-->
<define name="RADIO_MODE" value="RADIO_GEAR"/>
<define name="RADIO_AUTO_MODE" value="RADIO_AUX1"/>
</subsystem>
<subsystem name="imu" type="aspirin_v2.2"/>
<subsystem name="ahrs" type="float_dcm"/>
<subsystem name="telemetry" type="xbee_api">
<configure name="MODEM_BAUD" value="B57600"/>
</subsystem>
<subsystem name="gps" type="ublox">
<configure name="GPS_BAUD" value="B38400"/>
<configure name="GPS_PORT" value="UART3"/>
<configure name="GPS_LED" value="none"/>
</subsystem>
<subsystem name="control"/>
<subsystem name="navigation"/>
<subsystem name="ins" type="alt_float"/>
</target>
</firmware>
<modules>
<load name="gps_ubx_ucenter.xml"/>
<load name="airspeed_ets.xml" />
<load name="airspeed_ets.xml">
<define name="AIRSPEED_ETS_I2C_DEV" value="i2c1"/>
<define name="SENSOR_SYNC_SEND"/>
</load>
</modules>
... rest (commands, sections, etc)...
Also you don't need to add the ETS message to the periodic telemetry, it is sent with every measurement if SENSOR_SYNC_SEND is set.