I've heard of a few people playing around with a shiva, though I can't find the post right now. Hopefully someone will jump in here.
I've also heard of people attempting to elongate the port, to lower the box tune point, but again, I'm without a link or reference.
I personally have played around with replacing the stock sony driver with a a 4-ohm kicker solobaric s12c (the round ones). The amp handled it fine, but the speaker was not suited for that enclosure very well. It seemed to unload well before the Sony does. So, I'm back to the sony driver, with 3/4 lb of polyfill, and carpet spikes. Corner loaded, it sounds pretty good to me. Thinking of either DIY shiva or a SVS though (who isn't LOL)