The BOSE system in the 991-generation 911 is one of the more frustrating factory setups to work around. It's tightly integrated into the car's CAN bus and uses a proprietary amplifier that actively resists being bypassed. We've found the cleanest solution, and it's now our go-to for every 911 that comes through.

The factory BOSE amplifier is removed and replaced with a MOST25 DA-G2 optical converter — this strips the signal back to a clean digital source before anything else gets touched. From there, a Match UP 6DSP takes over, giving us full control over crossover points, time alignment, phase, and EQ without any factory DSP colouration in the signal.

The doors got a complete rethink. Focal B.A.M. butyl membrane was applied to both the inner door panel and the outer skin — effectively sealing the door cavity and turning it into a proper sealed enclosure. The difference in bass response and panel resonance is significant. Helix Ci3 drivers handle the mid and high frequencies, with Helix Ci5 subwoofers loading into the now-airtight door cavities.

We've done this upgrade across multiple 911s and other Porsche models. Sydney Porsche owners who've heard it tend not to go back.

Equipment:

• MOST25 DA-G2 — optical signal converter (BOSE bypass)

• Match UP 6DSP — amplifier and processor

• Focal B.A.M. — inner and outer door acoustic treatment

• Helix Ci3 — component speakers

• Helix Ci5 — door subwoofers

• (Upgrade path available: Focal K2 Power in place of Helix Ci3)