There is a difference (Now i use a nad 3020i)
I didn't know if my 3020E was in top condition (old amp, didn't have any to compare it to), so when i had the change of a 3020i i bought one (was a little bit cheaper than my 3020E), banana plugs,pre out and main in, sound is different from the 3020E, a bit darker midrange,slightly warmer sound.
Both amps are loud beyond there size and price.
I changed the metal brackets (those for the pre out and main in) and my cable from my usb dac to my amp, those actually changed the sound so i chosed (although it's a bit expensive) to buy the rca jumpers from audioquest to hear how it sounds.
At high levels the top sounds better on the marantz, a bit softer, the nad is atleast as loud (positon of the volume knob) mabye even louder, it's a dynamic and punchy amp with a good bass, i think/feel that somehow the bass changed when i got new cables, tried my old Qed cable to my dac to my amp, since it didn't made any noticeable change in the bass, i desided the rca jumpers was doing something to the bass, so i wanted to try audioquest's rca jumpers. The nad amp is definitely a musical amp.
The cable i bought for my pc was the same as i used for my cdplayer (inakustik premium), but there was a little difference in the thickness, the cable for my pc has a very good sound with no emphasis on any frequency's. Somehow i feelt the cable wasn't as neutral as the cable i used for my cdplayer.
The marantz amp is more like a well dressed suit guy, almost to perfect, nad is more the bad guy who love's to party......rock n roll.
it's a fun amp, love to play loud and has a good bass.