Here's how I sweeten and distort my metaloops. You might get good or better-
sounding results with something totally different.

FOR THE SONG ITSELF:
====================
Highpass over 60Hz. 24db per octave rolloff/slope.

Boost for 4db at 550Hz.

Lowpass under 4.6KHz. 12db per octave rolloff/slope.

Compress to a 2:1 ratio with an attack of 20ms and a threshold of 13db.
Threshold is gonna depend on how loud your song mixdown is, and I
unfortunately don't remember what RMS I normalized mine to, maybe -16db RMS?

I have a short echo set of 75ms, 15% wet, 100% dry after these in the chain.

FOR CROWD AUDIO:
================
Lowpass under 10KHz, 24db per octave rolloff/slope.

ACROSS THE ENTIRE MIX:
======================
Same highpass and lowpass values as the song track, but I highpass around
130hz here instead, still at 24db per octave.

I unfortunately don't have echo and reverb values for the master. GarageBand
only has cute knobs, not values. Both of them were set similarly, rather
short, rather dark (so roll off your highs to taste), with the song getting
about equal values wet/dry and the crowd getting ~3-4db more wet than dry.

This all sounds pretty good after you encode it to 22KHz and put it in-game.

-marf