nothing haha.. headphone out through T51.
although i use E6 with blue EQ when it is pairing with the ipod touch. its perfect to my ears.
i tried different amps/daps for it, but in the end.. the ones i expect it to sound better made it sound worse

like the hm602 for a DAP, it made the cd900st too warm which doesnt sound right at all.
toucan made it sibilant even on non sibilant recordings.
the pico made it really sibilant on sibilant recordings.
headstage arrow 3g made its soundstage too narrow.
i forgot how it sounded with ttvj slim and rsa mustang.
the t5 sounded like... nothing has improved, it just made the volume louder. haha.. i could be wrong though since i tested it with a very short time.