Kubi,
The knobs are Eagle Plastic Devices sold by Mouser. They cost only $0.50 USD each. They are also very similar to the knobs the we can get at our local Radioshack in the US.
Regarding the tube/trafo differences, I am going to be doing more listening in the near future and will post some sound samples too. If I had to make a reccomendation right now, I like the OEP's for their extended bottom end and the Telefunkens for thier better clarity and imaging, although I have not tried the combo of the two yet. I need to order some EH, GT, JJ, etc. tubes and try them out too. Hopefully I'll have something together next week, because I'm leaving on a business trip in a half hour.
Regards,
Chris