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Imperium
Old
A Thousand Lies
Clenching the Fists of Dissent (first four minutes)
Seasons Wither
Block
Beautiful Mourning
Bulldozer
The Blood, the Sweat, the Tears
Slanderous
Halo
Davidian

The problem with Machine Head (it's a good problem) is that a lot of their songs are epic and long that you can put so many of them as openers, but I truly think Imperium would be the perfect opener. Other ideas for openers, you can just switch them in my setlist, would be Clenching, Halo, Davidian.