I have had 3 different sergers ( upgrading each time ) My current one is a Pfaff coverlock 4852 and have found ALL of them are hard to thread or set up for a different stitch!
I think your best bet would be to keep your eye out for a used self threader, Babylock has a nice line up of self threaders. I may not be the best help as I just use mine once in awhile.