Adding an amplifier for sub-woofer duty.
For smaller events, the QSC PLD 4.2 works great for sub-woofer duty... however, a more powerful amplifier (better suited for sub-woofers) is added to our small amplifier rack. The QSC PLD 4.2 (that was used for subs) is now placed back into monitor duty with the other PLD 4.2.