The lower the frequency, the more omnidirectional, which is why home systems usually have one subwoofer you can stick behind the couch. High frequencies are not only increasingly directional, but they define the individual characteristics of the instrument.
If you filter out the upper harmonics, it's nearly impossible to distinguish between a flute and a violin playing the same notes, for instance. Bass frequencies provide the power, high frequencies define.
That's why bass sounds odd in stereo until you get used to it.
Add to that the fact that bass sound waves are very large (and we're usually pretty close to our amps) and unless you've got some kind of hairy monitoring going on, we're in precisely the wrong place to judge how our rigs actually sound to an audience.
I have someone else play my bass while I set the sound on my amps, making a trip or two out into the hinterlands to find the room boom, then swap places to fine tune the controls on the bass itself.
Tom Dowd said that it's easier to find what sounds like crap and filter it out than to enhance the good stuff. Saves a lot of time, too. On a parametric EQ, jack the level and sweep through the frequencies, and the crap jumps right out, believe me. Then dial down the level until it goes away.
I think of my Series 1 as two overlapping systems with individual controls, rather than stereo, per se. Makes it a lot easier to visualize the sound when setting up.
I rewired the 1/4 jack on my to mono, for gigs where I only need one amp, and to send a summed signal through a direct box into the board.
I use the 5-pin for stereo, either through two amps or to two channels on the board (I know it sounds weird, but panning too hard yanks the balls right out of the bass.)
Bass frequencies use over 90% of your amp's power, simply because it takes a lot of power to move a lot of air. The advantage is that you can pretty much set it and forget it.
I run the bridge pickup (treble) into two small cabs on either side of the stage, on stands. (A Carvin Stagemate and its extension, 100 watts per cab.)
The neck pickup goes into a Carvin 600-watt amp with 1-18 and 4-10 cabs.
Room boom is generally in the 250-500k zone, because most of the instruments share that frequency range. It's the bassist's playground, because between the bass drum(s) and bass, it's where the band's overall attack comes from. Too much 250k and it gets muddy, though.
Once I set up the bass (bridge pickup) to provide the thump, I don't touch it.
I hope some of this helps. Stereo is terrific, as long as you get used to the idea that onstage, you're in a lousy place to judge your own sound. Leave that knob alone, son.
(Message edited by Ed_zeppelin on July 26, 2015)