As a manufacturer, I find it hard to think he wants to charge you $300 even if it does go to the purchase price. Are you buying the amplifier new, used,? Is he offering the amp at a discount or retail price.
IMO the Pass is a better sounding amplifier that the Benchmark which is about average sounding IMO. BUT there are better sounding amplifiers than the Pass also. Not sure about the price point but we offer a pre-production hybrid stereo amp for $6500 100/wpc that we believe is one of the best sounding amplifiers you can hear as a comparison.
Happy Listening.