Cactus - your posts above were quite good, in my opinion.
A lot of times, folks don't realize how many low-end frequencies are too 'thick', and are competing all over each other, and when things then sound 'lost in the mix', they try all kinds of things end still end up with mush.
Take a look at the frequency overlaps between things like bass and drums, as well as any low-octave piano and bass. These are the most common low-end instruments that fight to be heard, because their frequencies are all overlapping.
I have a wonderful laminated chart that I keep posted immediately in front of me, to the right of my 2 monitors, that lays out the frequency ranges of various instruments. I simply searched the web and found it. They let you look at it online for free, and for something like $10-$20 they will send it too you. It's pretty good size, and I use it everyday.
The idea with all of what I am getting at is that many times, if you analyze the notes being played in the low end, you will find the ones that are overlapping, and then you can decide how to deal with it. Some folks try to boost above it, but I suggest looking at instead 'THINNING' some of the frequencies, notching out some of the frequencies, so that you still have a substantial portion of the original sound present, but just a bit 'lighter' for those particular overlapping frequencies. Another way of dealing it is to take a look at the low notes some instruments are playing.
For example, if you listen to Steely Dan music, you won't notice it immediately, but most of the time the keyboards are NOT including the typical doubled octave apart root notes of the chords, and in fact many times the keyboard player is only playing 3-4 note chords in the right hand, with only an occasionally needed single lower note. Another example is Genesis. They write their songs so that each instrument is given its own space, and it makes EVERYTHING stand out, with a GIANT sound. So, let the bass player play the low notes, let the keyboards play their own notes/chords, and leave the guitar player to their own devices. Without even dealing with EQ or compression yet, cleaning up notes that aren't needed will by itself make everything sound cleaner, crisper, and it all stands out better.
THEN you can look at compression and that whole end of things.
There are SOOO many ways of doing things, and folks are right, it is incredibly subjective, but regardless of the method chosen to 'fix it', mushy music is a lonely and soulless place to be. :)
Bob Bone