How do I pay?

Unless I could listen to the speakers in person, I wouldn't consider sending a cashier's check to somebody prior to having the speakers in my possession. And, $4K isn't something that would warrant such demands.
From my days of buying/selling watches, I have seen numerous posts about cashier's checks being bounced, as well as wire transfers. 
Unfortunately, we live in a world where a few bad actors spoil online buying, so I guess the seller is trying to protect himself.
One possible course of action is to ask if he has an Ebay, USAM, or Audiogon account, and you would be able to see if he has positive feedback.
B

See how trustworthy humans are. Who do you really trust? Why are we like this. Is i that there are too many thieves out there or are we all thieves under certain circumstances. 

@kjohn1234,

You can use Escrow.com to complete the sale. There is a small fee involved but atleast this gives you peace of mind against any possible fraud or defective merchandise. 

https://www.escrow.com/learn-more/how-escrow-payments-work/how-escrow-payments-work

If seller refuses to accept payment via escrow, I would walk away from this deal. 

I came across a seller who had a great price on a Shunyata Research Triton v1 and typhon.  He then made up excuses on why he didn't want to use paypal and said "I'll just send them to you and when it arrives, send a check".  Weeks went by and after a few calls he ghosted me and then I saw it listed again at the same price.  I reached out and asked what was up?  He then face-timed me showing his mansion and finally said "We are humans and you are going to have to trust me and just send me a check and I will ship to you".  Mind you, he had three feedbacks from four years ago - I figured he was couch surfing at his brother's pad and tried to milk me out of $2400.  Gave me a good laugh.

@lalitk +1

escrow.com is a great service but doesn't cost any less than PayPal. It seems to run about 3% as well. If the seller will not pay for one or the other service, and it makes financial sense,  offer to pay the fee yourself. If seller still says no, run!