Somethings I sell go in multiple boxes to avoid similar nasty jumps from rate to rate patrticularly when sending by air but to the buyer that is still one p&p cost so one total price regardless of the number of packages.
Ok so you cannot do flat rate if flat rate applies to all of the USA for these items.
Quote "And as far as "email me for a shipping quote" I don't have all day to go online and check all the possible shipping rates for each possible buyer" you are getting rather anti-customer focus with your tone.
Just do it as and when they ask not have it all prepared in advance.
You have two choices swamp the buyer or get them to ask, why not put 4 examples next door, 2 intermediates and furthest and specific quotes on request.
What about sellers of similarly large items, how do they do it, I cannot believe you are the only one selling sets of items that are bulky !
Strikes me you are more concerned about your 'perceived' hassle in sorting out the postal rates than what a customer would see as hassle, surely these items together are worth a significant amount and worth the effrort ?