Think i will post my humble thoughts on this vac and some alternatives later on another thread insted of hijaking your but ....
No reason you cannot fit them to any machine with afew fitting mods ...
I believe they use the same fitting size as a 7.2 so that would be a straight swap ...
No reason why you cant put two on one cord .... perhaps the guy that told you that was thinking in USA terms ... in the UK the each 6.6 will draw about 5 to 6 amps ...
They are 160 dollers on steambrite but by the time you ship them here +tax etc im sure the e-bay price is good ...
there seems to be no hako tube for hose attachment ... so to fit most machines you would have to get one welded on ... id say any local engineering shop will fit a 1.5 " tube to it for you ...
Good vac overall so snap them up before he sells out