So in comparing the D30 to my SMSL M8 I have to say that the one place I noticed that the D30 lacks is in voices.
Voices are recessed vs the M8, I'm not sure if its due to the internal filtering but its very noticable.
I have just been listening to my M8 for the last 5-6 weeks and I put the Topping D30 back on about a half hour ago.
As soon as I got to a song with alot of vocals (especially female Vocals) in my Discover weekly I noticed the vocals were recessed vs what i have been listening to.
I tried to turn the volume up but this doesn't make the vocals be at the same level as the rest of the music, its still recessed.
So I listened to the full song, plugged in the M8 again and am playing the song again now and its definitely recessed.
Now I'm not sure if the M8 has a more forward set of vocals or the D30 is recessed. This is just a comparison of the two.
For scientific purposes everything was the same and the M8 is in "Slow" filter mode. Now the D30 may be more flat or it may be recessed under flat.
But it is worth noting that the reason I took the M8 out of the box in the first place was due to voices being difficult to hear when I was watching the NBA finals on my computer.
I decided to "try" the M8 and basically I have left it since then.
I recently got a O2 Amp to compare to the A30 and they are virtually the same but the A30 has a greater degree of volume control with low power sources.
The headphones I am using are 1More Quad driver, Panasonic HD-10, Beyerdynamic DT770 16Ohm.
I have tested the same song with both amps aswell.