@ironic Here is my openmsx config for recalbox.

I´ve created a folder on : /usr/emulators/openmsx/bin/
I put my openmsx binary file form retropie inside.
Here you have the link
http://s000.tinyupload.com/?file_id=22889548546368582728

2 . This libraries are needed to launch the emulator.
Put them on /usr/lib
http://s000.tinyupload.com/?file_id=15973386028963335785

Launch the emulator with ./openmsx

After first launch go to /recalbox/share/system/.openMSX/
Put all this files inside the folder:
http://s000.tinyupload.com/?file_id=17148959869931873621

Create a folder on /recalbox/share/roms/msx inside it you have to put your Msx roms

Finally edit the file /recalbox/share_init/system/.emulationstation/es_systems.cfg

Adding this lines:

<system>
<fullname>MSX OpenMsx</fullname>
<name>msx</name>
<path>/recalbox/share/roms/msx</path>
<extension>.mx1 .MX1 .mx2 .MX2.rom .ROM</extension>
<command>/recalbox/scripts/runcommand.sh 4 "/usr/emulators/openmsx/bin/openmsx %ROM%"</command>
<platform>msx</platform>
<theme>msx</theme>
</system>

P.D. Maybe you need chmod 0755 -R to all files and folders and chmod +x to openmsx binary file.