Increase or Decrease "Harmonically Active" Frequencies

The human ear often uses the harmonics of a note to determine the fundamental even if it's not there! Getting rid of fundamentals is the easiest way to create space but it can make things thin quickly.

also if your speakers don't have a sub woofer they probably can't produce frequencies under 80Hz. Mine don't (when the subw. is off) and the sound doesn't suffer a lot.
 
I'm in the Baressi camp here, boost all the way.

The only time I really CUT using an EQ is on Overheads, sometimes Drum Rooms and GTRs.....possibly bass as well.

The rest is all boosting to get the MOST out of the instrument captured as possible... it's character, just as you said.

NSGUITAR has it exactly right.
 
I found a sweet spot in my piano around, 566 hz or so. Boosted it like 1.5 and it gave the piano such a warm depth to it and it sticks out just the right amount in the mix.
Check out this sample to hear what I'm talking about!
From my upcoming EP