數碼鋼琴錄音問題

事源係想用數碼琴錄野,但唔成功,所以想求救一下

器材:
Synth: Korg X50
Digital Piano: Roland DP 990
Interface: Roland Tri Capture
Software: Sonar X1 LE

以下全部都係用jet線做in and out

Case 1: Korg X50 line out, 正常錄到

Case 2: Roland DP 990 line out, 冇聲,interface signal燈唔著,即係冇signal

Case 3: Roland DP 990 headphone out, 有聲但低質素,同我插住耳機彈果時差一大截

Case 4: Roland DP 990 line out 入 bass amp,正常有聲,即係部琴的output應該正常

而家有兩個問題:
1. 點解我用headphone out入interface會有signal,但line out入interface冇signal?
2. 如果我真係居住用headphone out錄,有冇方法可以令個聲唔好失真?

麻煩各位幫忙解答,thanks a lot

just to check
1) are you connecting your Roland DP990 through the L/Mono output?
2) have you tried using another cable to connect Roland DP990 with the interface?

possible reasons I could think of are
1) internal resistance in your cable is high and the output from Roland DP990 is not enough to push the signals through. try a shorter cable, for example, and see if it helps
2) you may need to turn up the gain in your interface (if possible)