I can only speculate, but it is reasonable to suggest that with the 4.4mm balanced cable that comes with the660s you will find the AM3D able to drive it well and certainly significantly louder than your sound card. The quality of the sound from the Q5s/AM3E or AM3D is very, very good I feel and I have grown to prefer the AM3D as it is just so clean and controlled sounding. As it should be, the sound colouration that you will hear will be from the headphone and ever so little influence from the amp and DAC. That is how I hear it anyway. Throw in the very well implemented Bluetooth and you have quite the versatile little system that fits in your hand.
Thank you for answer.
Certainly I use it with balanced cable through 4.4mm, that's why I bought this DAC. I hope AM3D will better drive it, than AM3E. I didn't use regular sound card in past few years. The latest USB DAC (before Q5S/AM3E) was Apogee Groove and Chord Mojo. Both was louder, than FIIO with 660s.,
I know the difference between them, but I need a comparison between AM3E vs AM3D You have both (I think ), that's why I asked