I have some limited experience. I would say yes, do it because 1.) an Amp has a lot of heavy metals in it (both in weight and value ) and 2.) you don't want to take a chance of there being a problem. You don't HAVE to for US inbound I believe but again, better safe than sorry. You can also go to say the FedEx web site and get Documents, Tips, Est. Cost, etc. I would find a reputable Customs Broker (company) in NY that can answer all of your questions and handle most of the paperwork. Also, @nevusofota or @ZEN Amps might no more about this. Good luck.
It's been ages since I sold internationally so not sure about the current US situation - that's really for the buyer to figure out. I'm pretty familiar with the pain of importing into Australia though. High shipping cost aside, we get slugged with 10% tax, plus around $100 in bullshit fees. This is for anything over a grand, which is everything these days.
So total shipping and fees on a 3k amp is $700 - $900 easy. Then again we have AC-DC and The Living End, so it balances out.