I have been looking into Stylus RMX and have noticed at NAMM that they have released an even better version (V 1.7 with Time Designer) where you can map a groove from any existing audio loop onto the Stylus beat. I think as far as beat composing goes (especially if you are using Virus Control) you would be hard to match Stylus RMX as long as your PC and D/A is decent.
However if you are using one of the previous Viruses through standard MIDI a hardware beat box would be cool.