How can one detect the state of a headset and its buttons'?

For plugging/unplugging, I've found this partial solution:

# androidwish console, running on android device.

proc ::actionHandler args {
  # parse action here
  puts $args
}
borg broadcast register android.intent.action.HEADSET_PLUG ::actionHandler
0

# plug in headset (no microphone) and observe the following:
-1 android.intent.action.HEADSET_PLUG {} {} {} {address {} state 1 portName h2w microphone 0}

# unplugging shows a state change:
-1 android.intent.action.HEADSET_PLUG {} {} {} {address {} state 0 portName h2w microphone 0}
                                                                 ^
# state changed from 1 to 0 here --------------------------------^

# similarly, when plugging in a headset _with_ a mic, it shows up at the relevant property
-1 android.intent.action.HEADSET_PLUG {} {} {} {address {} state 1 portName h2w microphone 1}
                                                                                           ^
# here ------------------------------------------------------------------------------------^

# but when I try to register a microphone button activity listener, it doesn't seem to work:
borg broadcast register android.intent.action.MEDIA_BUTTON ::actionHandler
1

# pressing the headset's button does not do anything. Tried with different microphone headsets, still nothing.

# tried an activity
borg activity android.intent.action.MEDIA_BUTTON {} {} {} {} {} ::actionHandler
1

# no callback was trigger

1. 3.5 mm Headset: Accessory Specification
2. Headset Expected Behavior
3. ACTION_HEADSET_PLUG
4. ACTION_MEDIA_BUTTON

Actually, to be usefull, a virtual event should report both the ON and OFF state of the buttons, so that the duration of the press could be determined for various actions to be called, as specified in (2) above, e.g.:
One button audio A function

I read here that there might be a need to include something like the following in AndroidManifest.xml:

  <receiver android:name="tk.tcl.wish.AndroWish" >
    <intent-filter android:priority="1000" >
      <action android:name="android.intent.action.MEDIA_BUTTON" />
     </intent-filter>
  </receiver>

Regarding the HEADSET_PLUG event you might use the event command
to make it into a virtual event in the handler procedure of that
broadcast receiver.

However, for the MEDIA_BUTTON, don't expect me to add a special
broadcast receiver tag in AndroidManifest.xml for a plain AndroWish.
This clearly is something which has to be done for a separately
bundled App e.g. using the AndroWish SDK since it's an intervention
in the overall device user experience despite the priority field.

I see.
I haven't tried to create a special androidwish for this yet, as I need to upgrade
the installation of the Android SDK on this machine.
I'll try it, and will report back, in case someone else finds this info usefull.
Thanks!

It seems like just adding a <receiver> tag in the <application> section of the AndroidManifest.xml is not enought to make it work. 
Tried also to see if any permissions are needed/defined for MEDIA_BUTTON or anything like it, but there doesn't seem to be any.
Any suggestions?