These last couple voicings are really just for fun, but I have used them in some of my tunes and I've also heard some band use these or similar voicings.
I may have said "Major Minor 7" in the video but the chord is in fact a Minor Major 7. That just goes to show how well my brain works while I'm talking to a camera :-P
This voicing is as simple as taking your minor traid and moving your 3rd finger back one fret.
As for the dominant 7 chords, they are a little weird for the chording hand.
I've included voicings for:
7 #5 b9
7 #5 #9
Make sure to avoid the A string in these voicings.
These dominant chords are all just extra voicings that you can mess around with and may are may not be usefull for you in a metal setting.
I will say though that I have used these chords in some of my prog metal tunes.
Have fun with these voicings and I'll see you later!