For a 6-item study, I think MaxDiff showing 3 items at a time could work. Also, paired comparisons could work. Our MaxDiff software supports either approach.
Warning: do not try to show 4 or 5 items per set if only 6 items are in the study! Bad results. The software will warn you if you try to do this.
If respondents have the patience to answer enough questions such that each item appears 4 or 5 times, that would be good from a statistical standpoint. True, most of your gains would be had by showing each item 3x, but there would be some additional resolution by asking each item 4x or 5x.