I bouced back and forth between these two models when I was trying to decide which one to get. From what I have read from Kicker reps and competitors,
2006 L5 = 2005 L7
I can't get anymore specific on what has been upgraded internally, so you may have to take that with a grain of salt. I am well pleased with my 06 L5. The price difference between the L7 and the L5 was about $50 when I was shopping a month or so ago. I opted for the L5 because I have a 600w amplifier and decided that I'd rather push the L5 to it's fullest rather than underpower the L7 by 150wrms.
So, to answer your question... I guess I can't give any specifics on the differences between the L7 and the L5.
If anyone knows, it would be interesting to find out.