Is an add-in/external sound card necessary?

[chiller15]

I have recently purchased a pair of Sennheiser HD599 SE headphones, and they're great. When plugged into the jack of my Asus TUF Z390M-PRO GAMING (WIFI) motherboard, with an onboard Realtek S1200A soundcard, the audio levels are loud enough that maxing them out is uncomfortable. I was initially concerned that it wouldn't be able to drive the headphones and they'd be too quiet.

 

I do have some questions though, as my knowledge in audio is quite limited:

1. Does an add-in sound card or external AMP/DAC only increase audio levels, or does it also increase audio quality?
2. If there is increased audio quality, would a non-audiophile (such as myself) be able to tell the difference in games?
3. I have a very basic pair of Create T10 2.0 speakers on my desk, which have a headphone socket. Is this just a pass-through, or would it have some effect on the quality of audio? Also, since these speakers have separate volume controls, do they constitute as an AMP if headphones were plugged in?
4. I purchased Dolby Atmos for headphones (it was on offer for <£5) - some external sound cards/DACs (like the EPOS GSX range) have additional 7.1 capabilities. How does this differ from Dolby Atmos? Can they be used together, or are they exclusive, where enabling 7.1 on a soundcard replaces the Dolby Atmos setting?
5. I have a another pair of wireless Sennheiser Momentum 3 headphones, which can also be used wired. If I used them wired, do they pull their power from the sound card, or from the built in battery?
6. I've noticed that the sound profiles are very, very different between the 599 and the Momentum 3 headphones, though I don't know exactly what contributes to this. Obviously one is open and one is closed, but the 599 sounds much bassier and more...I don't know, just more? Even spoken audio sounds more like someone talking close to a microphone, whereas the M3s sound more "natural". Surely there's more to it then just open/closed and more bass?

I hope that all makes sense.

[mariushm]

1. The onboard sound card is pretty decent already.  An external amp/dac would increase audio quality a bit because less electromagnetic interference from all the components inside the case hits the audio chip and the traces on the motherboard. 

2. You probably wouldn't notice it.

3. It depends on the implementation.  The speakers will have an audio amplifier chip in them but headphone output depends on implementation.  Some audio amplifier ICs have a "headphones" mode so they'll have a headphones amplifier section ... other designs just skip the audio chip and connect headphones jack directly to stereo cable going to pc. 

4. No idea... but I think it would be waste of 5 pounds. 

5. headphones shouldn't need power to work when connected to pc using regular stereo cable. The battery is needed to power the radio receiver that receives the digitally transmitted sound, the DAC which converts the digital stream to analogue audio, and the audio amplifier which amplifies the analogue signal to work on speakers.  if you plug in using regular stereo cable, you already get the amplified signal, so the receiver and dac and amplifier are not needed.

6. yeah, the shape of the part that covers your ears, the foam used behind speakers, the shape of speakers, the membrane used inside the speakers, lots of things affect how the sound comes out some speakers.

[Tigerleon]

25 minutes ago, mariushm said:

An external amp/dac would increase audio quality a bit because less electromagnetic interference from all the components inside the case hits the audio chip and the traces on the motherboard. 

And drive harder to drive headphones 10x better than onboard.

But in this case the Sennheiser HD 599's aren't that hard to drive.