Sorry, I'm basically just being overly technical here.
Most people refer to the single-channel Falcon head as a DX2 for lack of any better reference. Epson only called it a MicroPiezo head.
The three-channel Falcon head is officially the MicroPiezo DX3.
The two-channel head used in most Falcon II, Mimaki and Roland printers is from the Epson 10000, and that one got nicknamed the DX4. Epson just called it a MicroPiezo head.
The eight-channel head used from everything from the Epson 4000 to the Mutoh ValueJet and every Chinese printer in between got nicknamed the DX5 since it was the "fifth generation" head. Epson called this one the MicroPiezo AMC.
The repackaged eight-channel head used in the GS6000 and new model Mutoh ValueJets is still called a MicroPiezo AMC by Epson. Mutoh calls it something entirely different. Everyone else calls it a DX6.
The latest Epson head, the 10-channel one used in the Stylus Pro 9900, is called the MicroPiezo AMC. Everyone else calls it a DX7.
Confusing enough?