Pulling the trigger on pricey equipment

If he is 30, that seems fairly solid. You should also be speaking with him by phone to get a better feel. Paypal is probably your best option for payment.

+1 on what Roxy54 said. I always want to talk on the phone with someone from whom I'm buying something expensive. Arranging palletized shipping is not something I'd want to be nonchalant about. Paypal offers the most buyer protection of any payment scheme I'm aware of when purchasing from a private seller.

If you're that concerned, then don't do this sale and wait for the speaker to become available within driving distance so you can make a face to face transaction.

There are 'Escrow' services. The service holds the money and ony pays it when the buyer gets the items.
Usually escrow services charge a fee. and you would have to do due dilligence on picking one both you and the buyer feel safe with.

Any feeling of worry I would hold off and wait for some near enough you can go there.
Paalletizing speakers is a big deal, and the shipping company has to be really great. Any mistakes and you get busted junk.

The most I have spent here is $2,400 and that was delivered by the owner to my home.
I would be pretty worried with a lot more than that floating on a promise cross country.