The problem with the widget world system etc is that you cant apply a constant pressure for dipensing like I can with my pub gas bottle and regulator. But the pub bottle is not easily taken to a party etc. So after a lot of searching I found this:
http://www.magnetventile-shop.de/zubeho ... 87057e65cc
It fits the new style thread on the 60L aluminium sodastream bottles and the regulator attaches to the other end. It works perfectly.

I did originally buy another adapter from a UK company which was milled from aluminium but it was poorly manufactured and leaked gas. When I emailed the company about the problem, they accused me of damaging it. So found this instead and German engineering seems to be the way to go.
Hope it's of interest.