I have Focal 165 KF and CV1 speakers in my X. When powered well, they produce really clean mid and high range. I would highly suggest a BSW sub and a sub amp though to fill out the rest. What sub do you have?

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Black '01 X5 3.0

Sound: BSW sub box, Alpine PDX 4.100 and 2.150 amps, Focal 165 KF and CV1 speakers
Suspension: Eibach Pro Plus springs, sway and anti roll bars, poly control arm bushings, Bilstein HD shocks/struts
Exterior: Led brake lights, clear markers, black kidney grill, angel eyes