Cubase SX3 as a drum editor is not exactly what i would call "flexible". It CAN get the job done, but only if you put in the hours to properly program each drum sound.

The 16 step sequencer is designed more for synths rather than drums. Actually using that 16 step sequencer as your only tool in the kit for making drum patterns will dissapoint you im sure, but as mentioned above, what I do is re-wire my drums thru Reason, sync the audio outs in reason to audio-in channels in Cubase and just record when im satisfied. I think everyone can agree with me that when you start with reason for drums, using anything else seems counter-intuitive.

The second option is something like the Drumazon. That doesnt read samples, and only has 909 drum sounds but has a pretty cool step sequencer.

If i were you, i would just rewire reason, thats what I do.

I use cubase SX3 mainly for sequencing, recording and programming synths. I rewire it to Reason mainly for drums, while also rewiring Ableton for loop manipulation.