That bar is most likely the tension bar that keeps the trunk lid up. But I could be mistakened. That bar isn't nesscary but it is nice to have. So one solution could be removing the bar. The better solution would be what integraz92 said. Make some spacers for the speakers, and hopefully you wont need to make them so big that you will have clearance issues with the speaker cover.

If you dont know, the spacer is just like a washer made from MDF or whatever material you like to use. It acts like a thick washer that lifts the speaker off of the deck.