You will have problems with any aftermarket speakers due to the fact that the stock amp does not supply adequate power. The BSW package is specifically meant to be a plug and play solution. If you want other aftermarket speakers, and you are willing to install an aftermarket amplifier, there are many speaker sets that are better than the ones you mention. The Infinity Kappas have good reviews, but you will need an aftermarket amp to get the full potential.

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2004 BMW X5 3.0i - Mine
2011 BMW 328i xDrive - Hers
2002 BMW 325xi - waiting for a new owner