Good thread idea warpdrive,
As a shipper I can tell you that the shipping companies are good at making things clear as mud to us.
Answers change when you ask different sources, and those policies vary country to country. By far the most frustrating can be when customers see charges that we never see when obtaining quotes.
One interesting detail is that "ground" or "standard" shipping is often handled differently from those considered "express" or "expedited" services. Anything which travels by air tends to qualify as express. For FedEx that would include both "International Economy" (for small packages) and "International Economy Freight" (for palletized shipments). The transport charges are typically higher, but the additional fees can in fact make the delivered costs much closer if not flip them. For Canadian customers, also keep in mind that on FedEx's International Economy Freight FedEx will add both a higher fuel surcharge and ~$110 residential delivery charge. If you can either ship to a business with a dock or opt to pick up your shipment from the local freight terminal you can save $100-150. Each person can decide if that savings is worth the added effort and time to transport large, heavy speakers.
US made speakers and subwoofers (per NAFTA's definitions) will avoid duties, but not taxes. Unfortunately the "best" shipper to use is not always the same for every case, so don't automatically dismiss an option from a single bad report, especially in a very different location or type of service or product.