Ge that's faint for 20 seconds @ 1600 & F/5.6! ... I'm surprised. Perhaps just nights brightenning up in software? For example, here's
a 20 sec, 1600ASA, F/4 shot I took a while back (stacked, but individual exposures only 20 sec - stacking was using average). So you should be able to push some more brightness out of your image somehow..
But hey, at least you got something!
There's definitely a milky way in there.