Im purchasing a leisure bay Santo 78"x78" max full will be about 3500 lbs., We are mounting it on a existing deck 29' long and 8' wide about 14' in the air. We have ledger mounted to house and 2x6 joist ( every 16 oc ) with the support and beams being 6x6 every 5' , resting on 6x6 beam the 29' long. ( also beam ( or seal) is mounted back from the outside about 1" Can I just brace up the 2x6's from the bottom with 3 sets of 6x6 beams , with doubled 2x10's on each one would basically put a 80"x80" frame under the existing floor joist ( so they wont have any pressure on them ) or maybe remove decking boards and then double each joist that will be under tub?
thank you

Best to check with your dealer where you're purchasing your spa and/or your local building official.