It wouldn't surprise me at all if these were dumped somewhere...that's what I would do with huge speakers like that if I didn't know what they were. Or maybe they'll call Soundlab to ask about value, instructions, etc
I'm sure you called Soundlab already to alert them of this.
Also, I would check the local craigslist...they might pop up for sale there.
I read of a free service that is like an ebay items for sale notification search but it scans ebay, craigslist and a few others and if soundlabs ever do come up on the local craigslist where the theft occurred you can be almost certain they are yours. If you want me to search for this article to get you the URL let me know and I'll do some digging.
Also...ebay has something called a 'want it now' feature where you post a wanted ad that people can scan and get in touch with you if, say, you're looking for a pair of Soundlabs. You should submit one. If a thief wanted to sell these on ebay that would be the more discrete way of doing it rather than posting them for sale.
If your car was hooked to the trailer, could your own auto insurance cover these by any chance?