1. Bridge Pickup Swap: Replace the stock pickups with high-output humbuckers that can deliver a more aggressive and distorted tone. Popular choices for modern metal include Seymour Duncan JB, EMG 81, or DiMarzio Super Distortion.
2. Lower Tuning: Modern metal often utilizes lower tunings like Drop A, Drop B, or even lower. Consider adjusting the guitar's tuning to match the desired metal subgenre.
3. Palm Muting and Heavy Picking: Palm muting and aggressive picking techniques are essential for modern metal. Practice developing these techniques to achieve the characteristic rhythmic patterns and chugging sounds.
4. Distortion and Effects: Use a high-gain distortion pedal or amplifier to achieve a saturated, distorted tone. Experiment with different pedals and amp settings to find the right balance between distortion and clarity.
5. String Gauge: Opt for heavier strings (10-52 or 11-56 gauge) to withstand lower tunings and provide a tighter feel for heavier riffs.
6. Guitar Modification: Consider installing a Floyd Rose-style tremolo system for added versatility in creating vibrato and dive-bomb effects, which are common in modern metal.
Remember that the key to using any guitar for a specific genre lies in experimentation and finding your own sound. With the right modifications and techniques, the Gibson Classic and Classic Plus can be adapted to play modern metal, although they might not be the ideal choice for extreme metal subgenres.