Bruce, welcome. If you're considering the relative power ratings between the 475 and 675 as a determining factor, the difference is trivial. 90 watts provide for only about 0.5dB more loudness on brief peaks than do 80 watts, an insignificant amount. If the 7 rather than 5 channels which the 675 has, or some other feature is very important to you, that's a different matter. Either of them can power the Axioms well unless you intend to listen at extremely loud levels or at a great distance.
However, my own suggestion would be to consider a unit(e.g., Denon or Onkyo)which has Audyssey auto-calibration and room correction, rather than the Yamaha YPAO. If your budget for this is in the $400 range, you should consider a factory refurbished model(likely to be at least as reliable as a brand new one)from Accessories4less. The
Onkyo 709 is a very good buy.
