[Envyous]

I currently have a DT990 Pro 250ohm together with a Asus Xonar Essence STX on my PC. First question is, should I have an AMP/DAC/whatever for this setup for better sound?
 
I am also interested in using the same headphones on the go (iPhone currently) and, most imporantly (most of the time) at work (stationary PC with motherboard sound output only). What amps would be best for this?
 
I know "some" of the amps has DAC. Is it worth having? I guess you can't use the amps with DAC on a phone because they require an USB output?
 
I am most interested in FiiO amps because I hear they are affordable and great. You do not have to find one that fits all use cases, I am willing to buy more than 1 amp if it is required.

 

[Ventace]

I currently have a DT990 Pro 250ohm together with a Asus Xonar Essence STX on my PC. First question is, should I have an AMP/DAC/whatever for this setup for better sound?

I am also interested in using the same headphones on the go (iPhone currently) and, most imporantly (most of the time) at work (stationary PC with motherboard sound output only). What amps would be best for this?

I know "some" of the amps has DAC. Is it worth having? I guess you can't use the amps with DAC on a phone because they require an USB output?

I am most interested in FiiO amps because I hear they are affordable and great. You do not have to find one that fits all use cases, I am willing to buy more than 1 amp if it is required.

If you really want something from FIIO, I'd go for the E17k+E09k combo, or if you're poor, just get the E17k alone or an E10k.
Personally I'd use it with an ODAC+O2 combo

 

[PurpleAngel]

  I currently have a DT990 Pro 250ohm together with a Asus Xonar Essence STX on my PC. First question is, should I have an AMP/DAC/whatever for this setup for better sound?
I am also interested in using the same headphones on the go (iPhone currently) and, most importantly (most of the time) at work (stationary PC with motherboard sound output only). What amps would be best for this?
I know "some" of the amps has DAC. Is it worth having? I guess you can't use the amps with DAC on a phone because they require an USB output?
I am most interested in FiiO amps because I hear they are affordable and great. You do not have to find one that fits all use cases, I am willing to buy more than 1 amp if it is required.

 
The DT990 do have their positives, but there are better headphones.
 
There are better DAC/amps then the Essence STX, but they will cost you a fair bit more then what the Essence STX cost you, to make a worthwhile noticeable improvement.
And for that kind of cash, you can get headphones a fair bit better then the DT990.
I spend $306 to get an external DAC/amp (NFB-15) that is slightly better then my Essence STX
 
You might consider spending $10-$60 to getting better op-amps, for the Essence STX
 
For on the go and at work, you could use a FiiO X3 Gen II ($200), should provide at least a little bit better audio quality, then your iPhone and the X3 can be used as an external DAC/amp. with your work PC.