Remember that selenium toning affects the silver that is present in the neg. Where you have empty shadows (ie. clear film-base) there is no silver and therefore no increase in density from the selenium. The overall contrast is increased, as the difference between "no silver" and "silver plus selenium" is larger, but nothing is going to magically recover detail that you didn't place on the negative.
You could always try making a copy negative and reversing it, or make a copy of the copy. The quickest thing to try would indeed be using a harder developer, as many have pointed out.
Edit: I have just recalled that, during a 25 sheet try out, I seemed to get a slightly higher contrast result from the Adox MCC remake of the Agfa papers, than from Ilford. Perhaps that would be an option?