The Virus is beatiful and complex and a beast when it comes to polyphony and multitimbrality. I wonder what the A4 would add to that, with its four voices.
As for the Rytm, you’ve got an Octatrack. That can take you very far. It doesn’t groove like the Rytm and it doesn’t have the analog stuff going for it, so the Rytm can make your drums and your samples sound like the stuff of awesome.
But whatever you put into the Octatrack, if it sounds good to begin with, it sounds good when it’s played in the Octa as well. So if you’re into making your own beats, creating your own loops, fine tuning this and that, the Rytm is a good choice. If you’re more into loops, repeats, existing material and stuff, the Octatrack offers plenty.
I’d say explore what the Octatrack can do for you in regards to drums first, if no other reason than to find out what you’re really looking for in a Rytm.