Mark,
When you buy a new piece of gear, like a receiver or preamp, it is setup for a flat frequency response. But every room is different and depending on what objects you have placed in it (like, chairs, tables, coffee table, ETC.) will put peaks and dips into what should be a flat frequency response curve. You can correct this with acoustical treatments placed in your room, but this doesn’t usually get past the WAF. But now we are seeing more and more system's coming out with auto EQ’ing, you place the mic in your listening position and activate the unit, it will play a series of tones to evaluate your room. After it has finished its job it will plus or minus dB your frequency curve to get it flat.
Doing acoustical treatment is best, but sometimes not an option, so some thing like this is a grate alternative.