SlowPro - When you say you want to replace the "tweeters", you mean the speakers, right? "Tweeter" technically refers only to the teeny-tiny speakers that put out only high-frequency sounds. The front speaker sets in the VX have woofers in the bottom of the doors and tweeters up by the A-pillar.

If you are going to replace all the speakers, then it's fine to go with the lower-impedence Infinity's. The lower impedence will actually draw more power out of the amplifier. If all speakers are being replaced with the Infinity's, then you are fine. If you replaced only the rear speakers with Infinity's but left the front stock, the rears will be louder afterward relative to the fronts.