I use the 8 outs to make a track. I use the external effects on my HD recorder, so those outs are essential. I got guitar amp simulators and distortion pedels I like to use on my DRUMS bass, and samples. So having those 8 outs I can send different levels to stuff without 1 effect over the entier mix. I went to using my 1k for a while because it had 6 outs standard compared to the 2 on the 4k without the 8 output board.
The filters on the 4k are not the best in the world, but it has some odd filter types that make your drums bang hard. I'm still learning how to mix the filters in with my samples, but its a few for drums that make them smack hard. I sample everything. I have a keyboard but I barley use it.