There are a LOT of great vintage amps that will BLOW AWAY the dedictaed headamps that people rave about. Marantz (1060, 1070), Marantz receivers (2225, 2230, 2270), Sansui (au505, au5900, au7900), Tandberg 33012 Prte-amp, Adcom 565, and yes - lots of NADs (352, 350,370,372,325bee,1020b).
But the truth is it is all hit and miss... The vintage amps are finicky... some sound great with Grados some make Senns sing. Be prepared to be disappointed or blown away. But all that fun experimantation comes at a VERY low price.
My personal Nirvana..... Nikko NA-790 with Senn 600s - absolutely fantastic! And it sucks with lower-impedance cans. BUT it drives my Canton speakers to places that headphones struggle to reach.
Check out Ebay. Check out Craig's. My Nikko came delivered for $55 and sounds better than any headphone amp I have ever owned!