[Mobilex]

I already used the search function of this forum but I didn't find the answer so I'm asking here.
I bought a pair of Senn HD 598 after reading lots of reviews, they should be easy to drive with almost everything but when I plugged them on my computer (integrated motherboard audio) the sound was just weird and much different for what I read about them. Their should be weak or at least have an adeguate amount of bass but instead, they have a really bodied bass response (not kicking but soft, still too much) and the mid-range is harsh and confused, the vocals are not sharp as they should be and are like subdued. I'm sure that is not a problem of this headphones because using my Galaxy Nexus the sound change in better and opens up, the mid range sounds good and vocals are just like they should be. 
I listen to high quality format such as flac and MP3 at 320 mbps bit rate, I use foobar2000 as music player and my motherboard is an Asrock Z77 Pro3; I don't use any kind of filter, enhanching or SW EQing.
To find a solution to this problems I bought a Xonar Essence STX but is not arrived yet. Anybody knows how the Xonar and the HD 598 sound combined? Should i buy another another Amp? (The STX already have a headphone AMP).
I already read the thread about the Xonar but for this headphones do you suggest to change the OpAmps? 

 

[PurpleAngel]

Your "bass" issues sounds like the motherboard's headphone jack has a high impedance issue.
 
The Essence STX should improve the sound quality of the HD598 over using the motherboard's headphone jack.
 
Did you update the motherboard's (on-board) audio software to the latest version?
http://www.asrock.com/mb/Intel/Z77%20Pro3/?cat=Download
But when you install the Essence STX your going to disable the on-board audio anyway

 

[Mobilex]

Did you update the motherboard's (on-board) audio software to the latest version?
http://www.asrock.com/mb/Intel/Z77%20Pro3/?cat=Download

Yes, but the sound didn't change.

 

[AaronR]

could it be a faulty adapter?
 
I just plugged my HD 598's into my laptop which has a Conexant SmartAudio HD card, and it sounded fine, minus the EQ'ing I prefer.
 
Anyways. There was a video floating around of a HD 598 adapter that fried this guys memory card. I just wonder if that same kind of interference could possible produce other effects, like what you're experiencing.

 

[PurpleAngel]

Quote:

Yes, but the sound didn't change.

Guess it is an impedance issue.
The Essence STX has impedance of 10-Ohms.
Where as your motherboard could have an impedance from 40-Ohm to 75-Ohm (guessing).
So the 50-Ohm HD598 should sound better plugged into the STX.
 
Op-amp wise, the AD797BRs seemed to be well liked for the STX (it's what i use).
 
This thread is a good place to post questions about the Asus Xonar Essence sound cards.
http://www.head-fi.org/t/421890/the-xonar-essence-stx-q-a-tweaking-impressions-thread

 

[Mobilex]

I tried my HD 598 on my Netbook (asus 1015pn) and the vocals were still not sharp as you should expect from this cans and with some songs I noticed a lot of distorsion (e.g: My Dads Gone Crazy - Eminem)
With the Nexus using "powerAMP" the vocals are good, the sound stage is acceptable, overall I did not notice any problem
 
 

Guess it is an impedance issue.

I don't know, the sound is not horrible, hashed or distorted but it's not precise as it should be. The vocals have a too soft texture and are confused. By the way the sound in gaming is perfect, wide, vocals are good, effects are really natural and sharp. 

EDIT: It's probably the impedance fault, since that was meant to drive speakers.

About the AD797BR, what kind of differences do they provide compered with stock?