#2
Cube's are generally good for metal, and since the GRX20 has humbuckers you'll be able to get a wide range of metal tones.
Washburn X50 PROFE
Dean Custom 450
Morley PWA Pro Series Wah
Big Muff Rams head
Zoom G2
Ibanez Phase Tone
Randall RG75 G3

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#4
HMMM, well i used to have a cube 60 with esp ec100qm and if you use the R-ifer you can get out a great metal tone for the price, also, try using it at higher volumes for great responsive gain.
#5
The GRX20 was my very first guitar.

Turn up the gain, turn up the tone knob on the guitar