If you want bass upgrade your speakers and get an amp or just do it the easy way and get subs. Just an aftermarket HU is not going to make that much of a difference on bass.
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1998 Pontiac Grand Prix GT
WizAired CAI, Impala 12" Brake Upgrade, ZZP Alternator Rewire and Voltage Booster, Rotated Dogbone Mounts, Kicker KS690 6x9s, JBL GTO427 4s, JBL P652S 6.5s
2001 Ford F150 XLT SuperCab
Stock, LineX, 212K