Parallel downloads/changing the "Max DL" value

There is a plugin for serienjunkies.org , which (the site) does not have a limit on parallel downloads since it only provides links, not files. So I usually have to select the links and Force Download them to just burn through the captchas all at once, instead of having it popping up every minute for half an hour. Unfortunetly I cannot change the value for "Max DL" in the plugin settings because the area is grayed out.

This screenshot should be self-explanatory:

How do I change the value such that I don't have to make Force Download? Is there a text file I could edit? What value would make the DL number unlimited?

serienjunkies plugin 1.1.3 allows you to increase "Max DL"