Wonder if just replacing the Magni with a Darkvoice 336SE tube headphone amplifier might do the trick?https://www.massdrop.com/buy/dark-voice-366se What sources or DAC, you us currently use, with the HD600 (besides the X5)?
The HD598SE comes with two cables.The 3m cable has the 1/4" plugThe 1.2m cable has the 3.5mm plugAlso comes with the 1/4" female to 3.5mm male adapter, for use with the 3m cable. Did not realize Sennheiser, until now, that started including the cable with the 3.5mm plug.
The HD558, HD598, PC360 all use the same 50-Ohm driver and can easily be driven by just about anything.Surprised you have not sold off two of them. If you remove the black rubber tape from inside the cups of the HD558, your going to get close to the HD598 sound. Here is a nice aftermarket cable for the HD558/HD598.http://www.ebay.com/itm/261255113290?_trksid=p2060353.m1438.l2649&var=560313338477&ssPageName=STRK%3AMEBIDX%3AIT I have the 60-Ohm Gemini HSR-1000, which is the...
With S/PDIF (optica/coaxial), Windows has a setting (S/PDIF Pass-thru) in the Playback tab that makes digital audio bypasses the on-board (integrated) audio features. You can get the Bravo Ocean for $80, usually with free shipping and maybe no tax.The Schiit Magni is $100-$150, ship shipping and maybe tax. Beyerdynamic headphone seem to respond well with tube amps.
The 50-Ohm HD598 are very easy to drive. Sometime in the future you consider getting this aftermarket cable.It's 3.5mm plug makes it a little easier to use, over the HD598 stock 1/4" (6.35mm) plug.With the stock plug you have to use it's 1/4" to 3.5mm adapter.http://www.ebay.com/itm/261255113290?_trksid=p2060353.m1438.l2649&var=560313338477&ssPageName=STRK%3AMEBIDX%3AIT
The SB-Z card comes with a nice CS4398 DAC chip, half-way decent headphone amplifier and the option of using SBX Headphone surround sound.As the SB-Z comes with Creative's Soundcore3D DSP, it should the best at working with SBX. Also here in the USA you can get a used SB-Z card for around $60, so in my mind I think of it as a good value, for it's price. I'm more of an Asus Xonar fan, over Creative stuff, so if I was going external, I think I would get the Xonar U7.