Computers are noisy environments and manufacturers are not going to sink a lot of money into the internal dac since this is not really a feature most buyers care about.  So yeah, the dac in the audio gd or matrix should be an improvement over your internal sound card esp. if you've ripped your music at redbook or above.  Insofar as the choice between the audio gd nfb12 or the matrix mini, I don't think the difference you point out (the frequency range) should be a deciding factor. 

I wouldn't put too much trust in the specs of such niche products as given by the manufacturers. Personally, I would go with the Matrix out of those two, but definitely avoid any IC opamp "rolling" or "Class A biasing" mods for it.

The M-Stage has a built-in DAC? I thought it was standalone...
 

I disagree, I've read that upgrading the opamp is the first thing many people do with their M-Stages. There is quite a selection of choices to roll, and they do make a difference sonically.

Hello, I'm new here. :)

This topic has probably already been discussed hundreds of time, but I've not found my answer yet... So, I've been listening to my K701 through an old Pioneer DC-Z82 for nearly two years now, we are very far from Hi-Fi and I grew tired of this "amp". So I've been looking for a cheap amp in the $200-$250 range and found these :

1. Matrix M-Stage

2. Audio-gd NFB-12

3. Little Dot MKIII

4. Bottlehead Crack

However I can't quite decide between them. I think the Little Dot is ruled out because I've been told it will not drive the K701 properly, higher impedance headphones are fine, but not the K701, same for the Bottlehead Crack (the Smack would be adapted but is way out of my budget).

So we are left with the Matrix and the Audio-gd. And I have a hard time chosing one, so I will ask some questions :

1. Is a DAC *really* necessary ? I use the output from my motherboard (Gigabyte GA-P55A-UD3) and it sounds ok, will a DAC be a notable improvement ?

2. Which amp drives best the K701 ?

3. I'd be inclined to choose the Matrix because of the frequency range of 10Hz-35KHz versus 20Hz-20KHz for the Audio-gd, is there a notable difference ?

If you have other suggestions, feel free to tell me. ;) I don't really care if the amp is solid-state or tube based, I just want the best bang for the buck.

Thank you :)