If they are in a sealed enclosure, the speakers will not be affected by the subwoofer. I had 6.5" coaxials in the back dash for a while and never had a problem. I wouldn't bother, though, as my passengers think my current setup sounds better anyways. I now have 6.5" components in the rear doors with the tweeters in the C-pillars. It take a lot less time to install and it sounds better.