The NG98 just arrived! I have to say that I'm very impressed so far. These 44 ohm Shure SRH840 headphones can make use of that whole 7 volt (peak) output under the right conditions.
Funny story. When I first powered the NG98 up and listened to a song it seemed like I was getting some odd distortion. But then a few minutes later after trying a couple of other songs I came to realize what I was hearing was detail in the first song that I never knew was there before! That's what I get for choosing Lady Gaga's "pokerface" for my first test song.
The NG98 showed its chops right off that bat.
With the Shures about 1/3 rotation of the NG98's volume control seems to give a good listening level with modern production songs. But with some older-production songs (Jerry Rafferty's Baker Street was one) are benefited from some bass boost that didn't make it into the recording.
With Windows 7, for the USB audio codec, the bass boost is at "control panel" -> "sound" -> "USB DAC (shows up when the NG98 is plugged into USB)" -> enhancements tab -> check box for bass boost -> "apply". Then at the bottom is a "settings" button where you can choose the crossover frequency and dB level of boost, then "apply" if any changes. The defaults from Microsoft at 80hz and 6dB. Most modern songs don't need boost with the Shures it seems from my listening last night, but a few are helped by 3dB. But some older songs like Baker Street are helped by 6dB.
With the 6dB of bass boost (80hz fc) then the volume knob has to go up to about 5/8 of the way with the Shures for average listening levels. With the 6dB of bass boost I can actually rotate the NG98 volume all the way - presumably 7v peak - and the phones are still wearable (although very loud!). I guess that gives me "an 11" with the NG98.
As time permits I'll open it up and see what's going on in there.
-agdr