The buyer is not 'unreasonable or irrational.' You said you had the manuals. Maybe he wants them in case he sells the amps at a later date, maybe, like me, he just wants the orignal equipment, boxes, packings and all else included. I lost the manual to my Nakamichi 700, got a copy from the company, but it's not the same, and I don't even buy and sell. Iif the buyer decides to take your offers that's up to him. Otherwise do the right thing. And if could be that he passed on other amps for sell just because you said you had the manuals and the other sellers did not.
Cheers.
Cheers.