To me it sounds like you're adding filters and EQ to enhance the sound of EVERYTHING, which is not really what you're supposed to do.
You use EQ to cut back frequencies when a specific range is too loud or conflicting with another instrument. For instance,
synth A has mainly mid high frequencies while a synth pad B has lots of mid lows AND mid highs.
If you played them together they would conflict because they're both fighting for the same range. If you used an EQ or filter to cut the mid highs (but not all the way, you still want some room to breathe) on synth pad B, you give synth A more room to cut through the mix.
That's the basic theory behind EQ for mixing. For mastering, if the mix generally is biased towards mid to highs, you can boost the bass, within reason so it still sounds balanced.
Yes I used synthesizers in my example, but this generally goes for anything especially if you're doing orchestral with instruments from different sources. Like they said above, stuff from the same library go fine together, but stuff from different sources don't.