Don, Nobby, Dave
Thanks for your great tips. I deduce I have been playing mostly in "dead" rooms, 'cause I'm used to compensate with the equalizer, and haven't found severe problems with increasing the volume. Where I have had trouble is getting a clean sound in places with huge glass surfaces, because of the numerous reflexions. First, the sound looses clarity, even in the neighbourhood of the area with the music, and second, just as Dave warned, there's a strong tendency to feedback, so I'm forced to reduce the volume. I guess it's better to renounce to reach the whole room and worry about a good sound near the music, right? Reducing gain in the high end frequencies seems a good idea and makes all sense. I'll try it the next time. Curiously I never felt the need of putting the speakers near corners to increase bass, maybe 'cause I bring a PA with a nice subwoofer.
Sometimes my ears sure indicate me that something is wrong, but I'm not always able to interpret what is wrong, neither to find the right action to undertake. Thanks again for your wise advice! :-)

-- José.