A reasonable rule of thumb (not to be taken strictly) is one voice per row. I would count the Salmple as more than one voice, though it's hard to put a precise number to it. The Lizard VCO is another. Do you need more than that? If so, maybe consider the Noise Reap Paradox and the WMD C4RBN. I have read that Optomix is difficult to get hold of these days...