Hi @DaveJZ, I've had the same problem recently. I shopped around and found out that Eva Air (a Taiwanese-based airline) allows 5 additional suitcases per traveller, at ~$200 per suitcase. You have an allowance of 2 free suitcases per person, plus additional 5 at cost. For two travellers it gives you a total of 14 suitcases, for additional $2,000.
I used extra strong boxes from Home Depot, with dimensions within the limits set by the airline.
At BKK customs they just asked what's in the suitcases; we told them we're moving the household from the U.S. to Thailand, and they just waved us through. We went to the Post Office at the airport, on the Arrivals level, and shipped them overnight to our final destination in Isaan for ~THB4,000, i.e. ~$130.
Advantages: your stuff arrives with you; no customs or duty fees; the transport cost ~$2,150 grand total, as opposed to ~$5,000 for the least expensive option I found with a shipping company.