Paying with a cashiers check? Need advice!

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.

I'm amazed how many people here are so quick to accuse the seller, with 18 years of positive feedback on Agon, to be a scammer. 

OP, have you just tried calling and speaking with the seller?  Maybe do a facetime call where the seller can demo the unit for you on the call?

Use the Escrow company and they should be able to accept a USPS money order. 

Or perhaps you have a friend or relative that lives nearby the seller that could pick up the item and ship it to you.  (??)
My advise would be if the OP doesn't feel comfortable with any transaction, just move on.  That's not to say the seller is automatically a scammer, either. 

The point is moot now as the preamp has been sold. Either the OP bought it or someone else did.

https://www.audiogon.com/listings/lisa8bfd-mcintosh-c-46-solid-state?refsource=hifishark