Resources!
The 400 has 8 buses that it uses to accommodate all the required resources. The default configuration is set to a 2/6 split meaning that 2 of the buses are reserved and 6 of them can be set for station and trunk modules (and a few specialty ones). In that configuration, the 400 can handle roughly 50 ip sets. If you require more, you may be able to change the split to 3/5 (I say may because it depends on whether you are using all 6 or not). It takes away bus 7 and gives you 3 reserved instead of 2. In that configuration, you can up the ip set count to roughly 95.
I'm sure there are a few who will chime in with the minute details of what you have to do and what to watch out for when you change the split but essentially you can get about 95 ip sets out of it.