The sound quality of the External Media Controller was great. After spending some time with the KOS-A200 system, the only concern we had was keeping track of the remote. Without the remote, there's no way to control the KOS-A200 and the external devices connected to it.
EFX HD4300After adding to the OEM radio, the next step was to upgrade the audio quality. The X5's factory amplifier provided adequate volume and clean power to the factory speakers, so we decided to leave the amp and speakers in place. The only thing the X5 truly lacked was low-end response. To overcome that frequency deficiency we added an EFX HD4300 amplifier powering a 12" DVC subwoofer.
With no room under the seats, we decided to mount the amplifier where the factory subwoofer would have been installed. While the available space came in handy, there wasn't much metal to actually mount the amplifier to. We used some sheet aluminum to bridge a gap inside the side compartment and, with careful positioning, mounted the EFX HD4300. Wiring up the amp couldn't have been any simpler. It had 8-gauge power and ground terminals that we connected to an EFX amplifier wiring kit. The amplifier also featured high-level inputs that allow the amplifier to be connected to factory audio systems without the use of RCAs. Since the OEM stereo was already amplified, we were unsure if the high-level inputs could handle the output from the BMW amplifier. Instead, we soldered one end of the Scosche RCAs directly to the signal input of the factory amplifier and connected the other end to the Scosche amp.
As cool as a custom subwoofer enclosure looks, they're not always practical in the cargo area of a SUV that's used for daily family errands. With that in mind, we decided to mount our subwoofer in a pre-fabricated sealed enclosure from Scosche. The enclosure is built to withstand a little abuse and is easily removed from the vehicle if necessary. The enclosure came wrapped in standard black/gray trunk carpet, so to give the enclosure a custom look on a pre-fabricated budget we had Carlos Aguilar of Vizualogic re-upholster the enclosure in matching BMW factory carpet.
Adding the EFX amplifier and subwoofer made a noticeable improvement to the sound quality. With the EFX amp turned three-quarters of the way up, we were able to turn the bass setting on the OEM radio down, allowing the stock speakers to play louder without distorting. The HD4300's crossover allowed us to adjust the bass until it was subtle and refined, complementing the factory amplified system nicely.