I am not familiar with a USPS method that offers true tracking - delivery notification sure, but not true tracking like FedEx or UPS. Ever since they lost a large mortgage payoff check that I sent via priority mail, in their packaging, with delivery confirmation, I will not use USPS for anything of high value. It has been 6 years, and that check has never shown up.
My shipments of expensive gear all go by FedEx Saver or 2nd day Air. It is my understanding that both of these methods are air shipments and are generally handled a little more carefully than ground. Lamm and Joule both recommend the FedEx air shipping methods for their stuff, not ground and not UPS.
Expensive and heavy stuff, like large speakers, can be properly boxed, securely strapped to a pallet and sent by commercial truck.
Regarding insurance, I recently ran into a situation where the local FedEx station told me "electronics may only be insured up to $1,000." I have never heard or been told that before, and FedEx has always been more than happy to take my money for higher insurance values. I didn't think to ask at the time, but maybe they have another category with higher limits that they use for "stereo equipment?" I need to check to see if my homeowners covers these types of shippments.