My interpretation of the original question was that a true sextet was being distinguished from some other arrangement of peaks which just appeared to be a sextet. A true sextet would appear to be a sextet under whatever magnetic strength you were using; an overlapping doublet of quartets (for example) which appeared to be a sextet at 200 MHz wouldn't appear to be one at 400 MHz or at 60 MHz, because the chemical shifts change (in Hz) with the magnetic strength, but the coupling constants do not.
The only ways I can think of to have five identical protons split a single proton would be if the proton was attached to an atom which could make six bonds, and those bonds would be in the shape of a pentagonal pyramid. The typical pattern of six bonds to a single atom wouldn't lead to identical coupling between any one group and all five of the other groups. Another possibility would be an atom which had five bonds to protons and a sixth bond to another atom with a proton, where all five of the bonds to protons could rapidly interchange.
If you try to do it with just hydrogen and carbon, you end up with different numbers of protons on adjacent carbons - 3 and 2, or 2,2, and 1. These would not be in identical magnetic environments.