Korg DW8000, Mono/Poly, MS-20...

well first of all, the L/R outputs are fairly quiet. a lot quieter than the 
headphone output.

second of all, you need to check the back of the synth and make sure that the 
'low/high' switch (next to the output jacks) is set to 'high'.

and also, it could be a matter of having patches with low oscillator volume 
settings. (check parameters 13 and 23.


let me know if any of that helps.
otherwise, get a preamp... or just turn the 'trim' up on the mixer channel 
for the dw8000.

-r andrew scott.