I would've said that the best bet for driving headphones directly in this price region would probably be the Revo 5.1, employing two 4580s (one per channel) for this purpose - but does it really? Anyone got a decently-sized board shot of the card (you can't see much on the promo pic)?
The ESI Maya44 appears to employ at least two opamps per output (at least I'm counting 5 stereo opamps for 4 output channels) and apparently does not have output coupling caps (places for rather big ones for out 3/4 and smaller ones for out 1/2 are still visible on the layout, but apparently they went DC coupled later). Aureon Sky/Space are also DC coupled from opamp to output, but only employ one stereo opamp for both channels which doesn't quite have as much oomph (at least a 100 ohm HD590 doesn't sound as dynamic as it should, while a 600 ohm HD540 is just fine); possibly this is more related to supply buffering than anything else, I don't know (that would be fixable with a soldering iron, at least). Also you'll get noticeable thermal crosstalk between the channels with higher loads. The Hercules Fortissimo 4 should perform about as well for driving cans, it's just that it's restricted to the generic VIA drivers which are perceived to be not so great (but it does cost quite a bit less).