I always remove the tubes and ship them separately by USPS Priority Mail. For an amp like that it is cheap insurance and the buyer would probably agree. The tubes will arrive before the amp as USPS Priority is usually about 2 days. At 80lbs I think you are over the UPS limit (which I believe is 70lbs). The question is not whether they'll drop your box, it's from how high and how many times :-) Honestly, if you ship your package across the country via one of the big shippers it will likely end up on miles of conveyor belts used for sorting and moving. Those belts are several feet off the concrete ground and packages can fall off of them. That is why UPS specifies that you pack your items to sustain a 3 foot free fall. I've had great luck with USPS Priority, but your package will be certainly too big to ship that way. I'd agree completely with those who advise a beefy outer box or crate for a component of that size. Probably the safest shipping method for a large heavy item is strapped to a pallet by air freight. I've used a terminal to terminal company called Forwardair, but they're only in specific metropolitan areas and they are only terminal to terminal. Check in your area for freight shipping options that will strap to a pallet and insure electronics for possible loss or damage.
Good luck, and good on'ya for asking first.
Good luck, and good on'ya for asking first.