Most of Headwhacker's fixes are already in rockbox git/gerrit. There are 3 issues with rockbox for DX90 I am aware of at the moment:
1. "Previous" button doesn't work as intended. Sometimes you can't switch to previous track. If you press and hold it in a menu, it does not auto repeat. Headwhacker mostly fixed this (sometimes I have experienced this problem with his builds anyways as far as I remember). This fix was backported to official git by DX50 guys, but it still needs fixing. I believe I've fixed it, but I need to test it a bit more.
2. Crackling noise. As far as I see it is related to android process scheduler. Headwhacker made many changes to fix this issue, I'm looking through diffs on his code and trying to apply his changes. When I'll be absolutely sure it is fixed, I'll think how to gracefully apply these changes to official sources. It would be a real pain to argue these changes, but at least it will let people build rockbox with extra patches from gerrit, just like last Cholero's build.
3. Sometimes when backlight turns on, volume goes to zero and then slides up just like when you unpause music. I'm not sure about nature of this issue and it needs some more investigation. It's rare, that makes debug harder. Btw, does DX50 has this issue?
When we're done with this problems, I'll try to make changes pass gerrit void. But that rockbox dev community… You know. They could demotivate even Steve Jobs, I believe.
Almost forgot one mini-issue: 4. Make random_folder_advance plugin scan only /mnt.