A few other differences is that the Axiom's are a bit more efficient at 93dB versus the 90dB on the 683's. In addition the crossover freq's 200Hz and 2khz on the 60's versus 350Hz and 4Khz on the 683's.

In regards to the min wattage rating, I'm sure it is related to clipping issues and underpowering high end speakers with cheap avr's at reference levels.

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