There is the Creative Labs Sound Blaster Z sound card,$84, comes with SBX headphone surround soundand a decent built in headphone amplifier (maybe not as good as the Vali). Otherwise I think the Xonar DX sound card (used $60) with an external headphone amplifier (Vali) makes a good combo
For getting Dolby Headphone with the Vali amplifier.
Get an Asus Xonar DG, DGX, DX, D1 sound card, they all come with Dolby Headphone and a DAC chip.
Personally, I would get the Xonar DX, it's PCI-E and comes with a CS4398 DAC chip :)
Plug the Vali into the line-output/headphone jack on one of those cards, plug DT990s into the Vali.
You will then get Dolby Headphone from the DT990s.
You could buy a FiiO E11K headphone amplifier, $60, plug it into the Xonar DX's line-output/headphone jack and plug the HD558 into the E11K.
The E11K's headphone output impedance is less 1-Ohm :(
You could also use the E11K with a smart phone or portable audio player.
Replace the Xonar DX with a Sound Blaster Z sound card, $84, it's headphone output jack has a 22-Ohm impedance,
not perfect, but a fair bit better the DX's 100-Ohm.
I own the Gemini HSR-1000, which appears to be a relabeled Pro 80.The Pro 80/HSR-1000 is a closed headphone and the Hi2050 is an open (semi-open?) headphoneSo yea the Pro 80 offers better isolation.I think the Gemini sounds a little better then my Hi2050.
I'm guessing a lot of A/V receivers do not publish the headphone output impedance because it would not be a flattering feature to brag about.250-Ohm headphone like the Beyerdynamics would be a good headphone for use with receivers You could try an Asus Xonar DG or DGX sound card, they are low cost, come with a basic head amp and Dolby Headphone.Can't be sure if it will not have the same issue as the on-board, or maybe not as much of a noise issue, or may have no noise...
Creative Labs Sound Blaster Z sound card ($84 USA)The Z, Zx, ZxR all use the same SoundCore3D audio processor, so there is no "gaming" advantage spend more for the Zx or ZxR.The ZxR does come with a better DAC chip and headphone amplifier, which should make a difference for sound quality (not sure how much). I'm not really knowledgeable about the Recon3D Sound Enhancer.