I am glad I started this thread as I found more interesting differences...
In addition to DAC+amp combos making a difference, I have found out that headphones (in my case K371 with dynamic drivers vs HE400SE with planar-magnetic) also make a difference in term of clues.
I excluded KTB and a10h from my latest round of testing (to save time). For this round of comparisons, I used 2 DAC and 2 amps with two different headphones.
As suggested by
@Jimbob54, I started by making sure both DAC are using 16bit 44100 Hz (CD quality) as default output format. I think (don't really remember clearly now as I forgot to write those down) previously my dac were all set to higher bit rate.
My findings:
******K371 headphones***********
*Topping E30 to Topping L30:
5ms - strange clue. Sync file has a strong single click and delay file has light click. Can't sense tonality change. Can't sense double clicks. Can pass using the single strong click clue.
2ms - can't sense clicks clues. Can't sense tonality change. Can't pass.
1ms - Sync file has a strong single click and delay file has light click. Can't sense tonality change. Can't sense double clicks. Can pass using single strong click clue.
*Topping E30 to Gustard h16:
5ms - able to sense double clicks clues and can pass.
2ms - not able to sense click clues. Can't really sense slight tonality change. Can pass about 70%.
1ms - Can't sense clicks clues nor sense tonality change. Can't pass.
*Gustard x16 to Topping L30 -
5ms - strange clue. Sync file has a strong single click and delay file has light click. Can't sense tonality change nor double clicks. Can pass using the single strong click clue.
2ms - slightly stronger single click for sync file. Not as easy. Can do about 70% correct.
1ms - strange clue. Sync file has a strong singleclick and delay file has light click. Can't sense tonality change nor double clicks. Can pass using single strong click clue.
*Gustard x16 to Gustard H16 -
5ms - no obvious clicks clues. A little tonality clue. Delay seems less clean. Can pass.
2ms - no obvious clicks clues. A little tonality clue. Delay seems less clean. Can pass.
1ms - no obvious clues. Get about 60%.
******HE400SE headphones*******
*Topping E30 to Topping L30 - able to sense double clicks clues. Can easily get 10/10 for 5ms, 2ms, and 1ms.
*Topping E30 to Gustard h16:
5ms - Can sense double clicks clues. Can pass.
2ms - not able to sense clicks clues.
Can't really sense tonality change. Can't easily pass.
1ms - strange clue. Sync file has a strong singleclick and delay file has light click. Can't sense tonality change nor double clicks. Can pass using single strong click clue.
Gustard x16 to Topping L30 -
5ms - able to sense double clicks clues. Can easily pass.
2ms - able to sense double clicks clues. Can easily pass.
1ms - able to sense double clicks clues. Not as easy, but can pass.
*Gustard x16 to Gustard H16 -
5ms - no obvious clicks clues. A little tonality clue. Can pass.
2ms - can't sense clicks clues. Sensed a little tonality difference. Can pass less than 70%
1ms - strange clue. Sync file has a strong single click and delay file has light click. Can pass using single strong click clue.
It would seems he400se is the better headphones to get more passing results than k371. HE400se passed 10 of 12 rounds. K371 passed 7 of 12 rounds.