forgot to mention this whilst we were chatting online.
I recently got asked to remaster some old cassette stuff for digital, and wow, I forgot just how bad old cassete was.
Firstly I used Izotop RX for intelligent noise, hum and pop/click removal (it really is faaaantastic software for the price)
After that I applied basic Mastering EQ and opened out the top and bottom end, used digital detailing to increase mid range perception, and then pushed up the levels with a nice maximiser.
Results were pretty good considering the original material.
If you don`t have RX I can run the files through for a cleanup, and leave you to do the EQ work to the rest.