Two Products of the Year 2026: With the QS series, ESX has introduced amplifiers that hit the mark in several ways. The QS-TWO and QS-Four are tiny retrofit sound boosters that offer two or four amplifier channels for powerful sound. The option of ISO wiring harnesses makes the QS-TWO-ISO and QS-Four-ISO plug-and-play solutions that are quick and easy to install. QS-TWO-ISO-BT and QS-Four-ISO-BT both come with integrated Bluetooth adapter for wireless music streaming in the highest quality. The QS series has also proven its worth as amplifiers in tests, boasting extremely low distortion and up to 90 watts per channel at 2 ohms for the QS-TWO. This is unmatched on the market, making ESX’s QS-TWO and QS-Four two very strong contenders.