Thanks for your input @ticol07. Its not the room. The issue is the same in every room including a sonicly dampened sound studio. I´we adjusted strings and pickups, to the best of my ability and they sound relatively similar without OD, but I´m sure its not perfect, so I´ll work some more on that. But the lower notes on the E-string still produce much more overdrive than, higher notes. I know my technique is not the best and in the heat of battle i tend to hit the E-string harder than the rest for some reason, which definitely adds to the problem. But to get anywhere near an even amount of OD all over the fret board I need to play very gently towards the low E and gradually harder op to really digging in on higher notes. I know deeper notes does produce more OD, but to me the difference is to much. The cheap DC9 compressor helps, but it kind of dulls my tone.
Ah OK, good for you if you already checked these problems.
So, yes maybe the compression can help. But still, without it there shouldn't be big differences in term of overdrive between your notes.
Do you have a recorder of some kind on which you could watch the level of your different strings. Sometimes you can get fooled : having the feeling your E string doesn't sound that loud, just because it's more bassier than the others. I noticed that on my jazz bass lately, and just by adjusting the pickups the tone was more even (with overdrive).
I, on myself, used the EBS multicomp at the beginning of my chain. It's simple, works well, and can be easily found used.
Now I use the compression of my amp (Spectracomp), but with a subtle touch. I like it better that way : I have a better difference in overdrive amount depending on if I play gently or hard.
The blend pedal trick is great too.
Other information : with the American Joyo, the Voice is there to focuse the overdrive on certain frequencies, so depending on its settings, highs will sound less or more distorded. You can for example set it to have the distorsion being more heavy on the mids and high mids but turning it after 12 and setting the drive not too high.
Edit: I'm seeing you also own a VT Bass -> the character does the same thing as the voice on the American, excepts it's set on higher frequencies.