The two SECN 6 firmware versions for MP02 are located at :
The version previously labelled "MP02 AWD" was re-named "MP02 FXS" in the SEC6 build.
SECN 6 is largely a rebuild of previous source code without functional changes, with the exception that for the FXS version the Asterisk functionality was simplified (e.g with the removal of the IVR function), because the underlying Asterisk version had to be changed and these functions did not port across simply.
But the normal telephony functions are unchanged.
The "MP02" and "MP02 FXS" versions differ only in the addition of the telephony subsystem, so I am interested in your comment about having limited success with the "MP02" version.
Are you using the telephony functions?
You might also be interested in looking at the Digital Library firmware for the MP02.
This is based on a more current version of OpenWrt and provides the AP and WiFi WAN facilities you mentioned.
The DL firmware is simpler than SECN (it does not include mesh networking) and has an updated User Interface.
The primary purpose of the DL firmware is to share digital library content stored on USB, but the use of this facility is optional.