The only polls that are built in to Discourse are single-choice, multiple-choice, and numeric. I suppose there would be 24 distinct voting permutations possible for each, so it would be possible to make a poll with each of them as a possibility. But then processing the results would be more complicated. Probably more trouble than it’s worth compared to just going back to “vote for any two to advance”. So far though I’m liking the current system because there is an element of comparing tracks outside of their groups, which gives a chance for the runners-up in a really strong group like C to advance rather than getting knocked out by the luck of the draw.