Room correction

[f1eng]

  It is typical to see 20-30+ db swings over a few Hz in the low frequencies because of cancellation and augmentation effects determined by room dimensions, moving the speakers will change the frequencies of these nodes but not eliminate or significantly reduce them.  Only with an infinite room - i.e. outdoor listening - do these issues vanish.

This is not quite right. The frequencies are determined by the room dimensions, so moving the speakers does not effect the room modal frequencies, but it does effect the extent to which they are excited. Correct positioning of the speakers to minimise excitation of room modes is very effective (but may end up with the speakers in a location which is not domestically acceptable).
The node is the location of the null point of a resonant mode, and the anti-node that of the maximum fluctuation.
Correctly placed Helmholz resonator absorbers can pretty well remove the effect of room modes, too, but they are very big, need skilful setup and may well not be very domestically acceptable either.

Personally I much prefer the passive correction to active, but it requires a lot more work and may not be very visually acceptable.