The refurb one is an Asus Q501LA-BBI5T03 (http://www.ebay.com/itm/Asus-Q501LA...ore-i5-4200U-Laptop-Refurbished-/321328516158)Since 6gb dimm don't exist i'm going to assume maybe there was 4gb stick and 2gb dimm, and u added the 2gb ram stick. the other 4gb stick could possibly be on the other side of the mobo like some lenovo units, or soldered on the board like some asus original zenbooks, or something else. I would suggest posting a picture of this '6gb' dimm so we could give you more information.
Well, considering the laptop only had one DIMM to begin with, don't think I'm losing anything.if I were you wouldn't do such a mix otherwise you would not benefit from Dual Channel memory mode. Only put RAM sticks in matching pairs