transformer headphone distribution

I saw these custom boxes at a studio one time and haven't been able to find any info for build.  I opened one up, just a box with a transformer (maybe 2) and a pot or stepped attenuator, high quality parts.  multiple boxes chained together with xlr in and out presumably powered by an amp in the control room.  the only thing similar I could find online is this: http://www.canford.co.uk/Promotions/2008/Canford/3.aspx

any ideas?  looks super simple to build but the parts cost may be prohibitive

Anyone?  is this a no-brainer project?  Why don't I see this type of thing marketed more often?  seems like an obvious choice in terms of quality and flexibility in the studio