Matrix's are separate out's from the FOH board that can have custom EQ, Gates, Comp's, FX's to YOUR liking. and keeps the FOH mix to the engineer's liking.
Microphones will never, ever, be more stable or reliable than a direct mix. You're asking a capsule to try to grab all of these different frequencies at one time, and when you have 60 subs blaring distorted 120Hz bass from the DJ's iPhone4 mix tape, your mic will be like "Screw this!!!!, All you get is a giant amplitude of 120HZ and won't capture the rest of the spectrum as accurately as a direct line will.
VST's are plugins so they would be plugins for Ableton but not Ableton itself.
If you're DJ keeps changing the levels, I would recommend a Gate and Limiter/Compressor to set the min and max level of your incoming audio. Be careful to leave plenty of headroom for actual dynamics, otherwise you'll just get a flat response and you won't have defined frequencies to play with.
If you're using Version 6, you'll need 64 bit VST's
Here is a DL link of all the one's I use (Freeware):
https://www.dropbox.com/sh/1f0gffulv1fu ... rCnua?dl=0
If you haven't added any special VST's into your Resolume folder then I would just copy and paste the afx folder and replace the one in your install directory;
C:\Program Files\Resolume 6\Plugins
There are some spectrum analyzers in there so you can really dial in your EQ's, Comps/Limiters, Filters, and Gates.
Add the VST's to your clips and click the little gear wheel in the pink audio tab next to the FX once it's been added. This will open up the VST.
Be sure to "Show Audio" to get access to your audio FX, audio FX is a small button in your FX tab next to Video FX.
Hope this helps.