Paying with a cashiers check? Need advice!

PayPal or stripe , otherwise No  buyers protection.

A Bank check is automatically debited from your bank account by the teller so the bank has no liability in the transaction once you walk away with the check.  Your account is debited period.  You can only place a stop payment on the check usually after 90 days.  So basically you can pay him instead through PayPal as a family or friend to avoid the fees as it should also be debited out of your bank account if you select that option.  I am not sure why he won't accept PayPal that way.

Using the Escrow is an option that I would present to the seller.  I believe you both need to register an account for this transaction.

Is there a local dealer in his area that you can call and pay a few dollars for where he can drop off the unit, get it inspected and shipped to you once you  pay the dealer his cut plus shipping costs and then the  dealer can hand the bank check to the seller?

IMO there is never only one special deal on something you may have to wait but they will come back up.

If you are so hesitant to do this then just pass on it.

Happy Listening.

I have seen accounts compromised and used the way you describe.

If he’s legit, it might be worth it for you to suggest a paypal payment and you split the difference in cost.

If he refuses, it might be better to walk away from "the deal."

Disclosure:  I used to do forensic investigations involving payment fraud.  

Ask Audiogon about the older feedback. I've done that before and got a response from them saying it all looks ok and nothing appears to have changed like email addresses or out of character activity. Audiogon has no interest in having scammers on here.

Based on his reviews it seems like he's a top notch seller.  However since the last review was in 2017, he may have gotten out of the game and this is just a one-off sale of his personal preamp.  He also may not want to incur additional fees beyond what he's paying for the listing.
The fact that the payment method says escrow.com but the text in his listing states cashier's check only is confusing, so here's what you do.  Escrow.com will cost $65 if he agrees with you to let you use it and pay by wire or (believe it or not) check or money order.  They hold the funds until he provides tracking information and they see that the package is delivered to you.  You have to read their terms but sounds pretty straightforward.  You both feel protected, that's what is most important!  
I just sold a Conrad Johnson preamp on here yesterday.  Within 5 minutes after I accepted the offer, the funds were deposited and available in my PayPal account.  There has to be a certain amount of trust in any business transaction, no matter what anyone else here has told you.  That goes for any business, anywhere and especially with online transactions.  That trust only comes from an individual's comfort level with the opposite party in the transaction and their transparency about the item for purchase as well as any other background info (ie:reviews) that can be obtained before proceeding with the purchase/sale.
My best advice is to be candid with him.  You cannot risk a check payment without an intermediary to make sure item is shipped before he receives payment.  If he says no, you move on.  But don't just walk away without presenting it to him first.  If he is truly the top notch seller that his reviews say he is, he will understand and try to work it out with you.  Or not.  At least you won't have to wonder if you could somehow have changed his mind.
Hope this helps you make your decision.