I used Pirate Ship a few months ago, for this exact type of situation.
With their discounted rates, I sent a highly modded amp to myself, OVERNIGHT, from California to Florida for $314 (with an abundance of insurance).......in a very heavy-duty amp case.
All of the ATA locks torqued down + heavy-duty zip tied, with the label affixed directly to the amp case. Handles on top, and sides of the road case, so no excuse to lose their "grip" on a cardboard box.
Less time for the people that work for UPS to do much except drive it to the airport, fly it to Florida, and then drive it to my house. Less than 24 hours, if you ship before Friday.......and only for about another $100 more than you would pay for 3-5 day shipping across the USA, for such a heavy package.