Drum program with more than 4 layers possible?

Yeah, you can submix everything together. Go to the Route tab of the pad mix. Select your pad and choose a submix (1-8). All kicks can be submix 1, all snares on submix 2, etc. Then when you want to mix the whole kit, go to the submix page in the Track Mixer.

Total work around, but you can insert effects on the submix for all snares or whatever that way.

Good luck.