I don't think the submission process is causing any delays...
Like Mokram mentioned, one of the obvious bottle-necks is the posting. Since djp doesn't have all the time of the world, it's obvious he can't handle to post mixes on a daily basis consistently. I agree with Mokram in that having more people (not many more) posting the mixes on the front page could help. Maybe try to organize it so that a mix gets posted every 2 days.
Now, about judging, I've noticed one thing that may slow the process. I opened the first 10 rejected mixes on the judges subforum and ALL of them had at least one vote that said "No (resub)", with most of the mixes receiving only "resubs".
Encouraging people to resub is a nice thing, but when you do this, the judging queue doesn't get any shorter than before judging the song (assuming most people actually resub). I haven't read the votes in detail, but maybe some of these "resub" posts are being too picky and could instead be changed to a Yes, which would slow the posting queue, but speed up the judging one. Otherwise, they could just be changed to a straight No. After all, no one says that a No means you can't resubmit.