More about volumes. The obvious, first though when you can’t hear a certain instrument in the mix is to increase the audio level of this instrument. Then others are not heard, those are raised. At some point everything is clipping, and even if modern audio engines are 32-bit (soon maybe even 64-bit) resolution engines, too much clipping and overdrive will just cause a big mush. So the final mix does not sound airy, rather harshly compressed, especially if a limiter is in place. If you look at such mixes, the tops are chopped off, rather than having nice waves that reach the upper part naturally.
So here are some more tricks how to get everything heard. This one is about how the loudspeakers work, especially with big systems. The low end has a slow frequency, so it takes a while for the cone to move in and out. The more material is pumping down there, the more movements the cones have to do, and instead of having a nice pumping movement that will move the air and get the feeling into the stomach of the dancing audience, it’s mostly a quick rumble with no emphasis on anything particular.
So. Let’s narrow down what’s operating down there. To start with, any other instruments and kicks and bass (with some exceptions) does not need to go down to below 120Hz. So just filter it all out with a high pass filter. The mix gets airier, and less volumes to drive the mix. Most other instruments don’t really have any interesting frequencies that low, anyway — with some exceptions, of course.
Secondly, and this trick could be used from time to time, just let the kick drive, nothing else. If you have a bass line, chop out or leave out any bass tones moving while the kick is doing its thing. With MIDI it is easy, but even with a pre-existing loop, with for example Ableton Live you could draw a volume envelope (see picture above) where the bass is not driving the cones while the kick is doing it.
I must again state that this technique will flavor the track — if you really want the bass line to follow the kick, which used to be common in ancient dance music, go ahead. Anyway, in many trance projects, this is a common technique, as well.
You could extend this to any other instruments, too. Ultimately this technique is heavily used in combination with a side-chain compressor so that when the kick is operating, most if not all the other tracks volumes are down via the compressor, leading to this hypnotic pumping sound that comes in and out of flavor from time to time.