This 600 should have the modified amp. Less than a year ago, Axiom sent me a new amp as my original amp in the 600 was defective. When I would adjust the gain knob even the slightest, it would jump in output like 20+dB's. Also, if I pushed on the amp plate in a couple of locations, it would do the same thing. I believe this new amp does not have the brickwall filter.

M80s VP180 4xM22ow 4xM3ic EP600 2xEP350
AnthemAVM60 Outlaw7700 EmoA500 Epson5040UB FluanceRT85