I feel your pain. I thought about this problem as soon as I bought my car. I lived with the Monsoon for a little while, but, I do need to go bigger. Plus I DO NOT want to have to put the T-tops in the back seat. I did A LOT of reasearch and I'm going with Blaupunkt speakers. They have a mounting depth of 2". So I'm going to make a custom box out of polycarbonate and mount them on the shelf behind the back seat. I did the measuring and it should work out nicely. If your interested, check out this link.
http://www.blaupunktusa.com/Blaupunk...er/ODw1200.htm
Hope I helped.