Doepfer

Well - Difficulty wise - all you have to do is desolder all the mini 
jacks and pots (you will almost certainly destroy the mini-jacks - 
no bad thing:). This is quite easy with a good soldering iron and a 
decent solder sucker, but is a bit tedious. 
Then you just solder connecting wires between the pots and your 
newly obtained 1/4 inch jack sockets. Attach the re-used pots and 
new jacks to the Faceplate (Schaeffer), then add knobs.
I just finished the A-116 and it took me about 1 1/2 to 2 hours 
total.
I am a slow worker :).
The face plates are designed with Schaeffer's own software - 
available at http://www.schaeffer-
apparatebau.de/English/FPD_index.htm
They cost about 20 - 23ukp or so a piece.
I used switchcraft 112a jacks (because they are the best) but they 
come in at about 1.50 ukp each.
The knobs - MOTM style cost about 70p each ( in bulk)
Then its just wire, solder, patience and determination to get rid of 
thoses darn mini-jacks.
If I have missed anything out or you have more questions just ask.
Steve M.