I've noticed a few Z series Zapco amps up for sale on ebay lately. There's a Z350 and Z500 which are almost identical looking to the Reference 350.2 and 500.1 although the casing of the amps is white and not the typical dark grey of Reference series amps I've seen elsewhere. They kind of look like the Reference 500.1M special edition which someone on here was trying to sell not too long ago. Does anyone know what these Z series amps are and how they differ to the Reference series?