I saw the curaengine interface. It looks to me that I'd have to build up a command line by specifying all of the settings that are normally in the profile and preferences. I'm just using the cura.py entry with a "-i -s -o " on the command line. The way I finally got it to work was to use an AMF file instead of multiple STL files.
My host program is my home-grown replacement for pronterface. I kept wishing for additional features in pronterface and finally decided to just write my own. I'm happy with the current state of it, but it's only ever been used with Marlin firmware, and although it's written in Python and wxPython, I've only ever verified that it works on an Ubuntu system. If you want to take a look at it, it can be found
here. Just a word of warning, though. I use github as the way to pass the program between my Windows machine, where I do most of my coding and my Linux machine where it will actually run. In fact I've never really taken the time to configure the slicers and such on my Windows machine so I don't even know if I can bring it up in that environment. The point is that at any given time, you might be getting a "development" version of the program.
I built the program around a notebook interface. The first page of the notebook is the log. The second page is the plater - similar to the plater in slic3r. The third page is the file preparation page where I can invoke a slicer (skeinforge, slic3r, or, now, cura), load G code directly, merge stl files into AMF files, edit G Code, etc. The G code can be passed from here to the print monitor page from where it is printed. This allows me to prepare a file for printing while printing is actually going on. The 4th page is for manual control - axis movement, heater control, extruder control, etc, as well as a widget for entering any G code command. Finally, the 5th page is for monitoring a print in progress. And I have a host of features in my to-do list.
I've always felt that this hobby was more about the journey than the destination. I'm never finished with the printer; there are always things to add, parts to design and print. This same idea now also extends to the software.