Thought I would follow up since this thread popped up again.
I have acquired a couple of Stax headphones, a traditional Lambda normal bias, a new Lambda SR 507, and an older SR 3n/5n, all great headphones.
I soldered the leads of a type 7 Stax transformer adapter to a standard banana jack headphone jack, and use the Manley as a Stax amp as well as a conventional headphone amp.
I also acquired a couple of single plate 5v 182b/482b amp tubes that work greaat in the Manley, and I can rotate them with the 300b for a different flavor. The 182b/482b aren't as spacious as the 300b, but probably have the cleanest headphone presentation through Stax headphones that I have heard, also with a lot of "single plate" DHT magic.
BEST is a matter of taste and definition, but they sure sound good.
In Santa Cruz, I have turned the AC heated 26/300b Hogan amp into a dedicated Stax amp with another 7 type Stax transformer adapter, also to wonderful effect.
I will be taking the Manley 300b preamp to the Head Fi meet on the peninsula Feb 11, 2012, and will be able to compare to some other types and let the attendees hear the Manley.