I have used the systems mentioned., and others. Prenect is by far the best, hands down, Also the support is outstanding. You would do well having me manag or at least setup your system
The system is Hotfolder based - so it would output to any printer - we have it outputting to 4 epson printers - I can't think of why it can't drive a wide format device? Mark Tonkovich from Heidelberg is on this forum - Post to Heidelberg - He will answer your question(s)
Take a look at Heidelberg Prinect! I have used Prinergy, Appogee, Screen - Like Heidelberg especially for the support - Easy workflow with the best imposition app - Signastation.
Softproof has to be done after converting the to pdf, for whatever workflow you are using - otherwise you are not proving anything! They are called proofs because they prove the file to be correct! IMHO
We soft proof our digital press files through our Heidelberg system - same work flow as offset