Hi Thor, nice to have your reply. I try to describe what i'm doing at this moment:
The output machine which you could assume it's a normal desktop DAC (usually with L&R 3pin XLR male as output sockets). That's why I make another cable (not the iFi one), say "L&R 3pin XLR female to 4.4mm male", to connect the DAC and Diablo. The "L&R 3pin XLR female" connect the DAC mentioned above, and the "4.4mm male" connect the Diablo as line in. Then found the problem mentioned by Bryce earlier "it makes sound but there was some hum and the bass was very obviously lacking".
If I wanna use my DAC (with L&R 3pin XLR male as output sockets) output to Diablo (as pure amp), any cable or connect methodology you are suggesting?
Look forward to your instruction. Glad to have your attention here