Give Me Room
Most of the problems lie in the bass, generally below 300Hz. There isn't space or time for an extended discussion of this subject here, but to briefly outline a very complex issue, the four approaches taken in most home audio systems to cure room/speaker problems (separately or together) are benign neglect, precise speaker/listener positioning, room treatment, and equalization. Moving sometimes works too.
Most audiophiles are in the benign neglect or positioning camp. Neglect often leads to compromises, such as the preference for mini-monitors with so little bass that they minimize the problems.
Choosing the right speaker and listener location is always important, and many serious listeners agonize over an inch or two this way or that. But rarely can you find a position for two speakers (or more!) and multiple listeners that optimize both bass and imaging. And in a home theater setup, positioning is further constrained by the location of a video display or projection screen.
Acoustic treatment is always a good idea. But while treating a room in the midrange and highs is relatively easy (even normal furnishings such as bookshelves can help here), effective bass absorption eats up a lot of space and often a lot of money. Little pillows in the upper room corners do nothing but make you feel better, and even the sort of bass traps commonly available to consumers are of limited value.
Audiophiles rarely choose equalization, largely because the tools available in the past have often resulted in more problems than they solved. But that is changing. New developments in digital signal processing promise to revolutionize the room-speaker equation. I recently had a peak at one of them, MultEQ from Audyssey Laboratories. It's built into several new Denon AV receivers. I expect to see it in products from other manufacturers as well, perhaps showing up as soon as next week's CES in Las Vegas. You'll learn more about it in my review of the Denon AVR-5805 receiver, which is scheduled to appear on this site early next week. Watch for it.