as GMG has already been quoted and you started your research into that as well, you might want to look a bit deeper into it as you might otherwise miss that you could do pretty much most of what you intend with a single installation of 1 software (and activating the respective licenses on it):
ColorProof and ColorServer can run on a single station (actually in a single GUI) and would do all you have in mind for proofing, separation, CMYK standardization and even color manage the Indigo to match sheetfed offset (or anything else for that matter).
As a quite inexpensive additional item you can have a look at GMG PrintControl as well, which adjusts your press settings (optimal density and the DESIRED PRESS CURVE in your Rampage). Works like a treat and in a matter of hours you can print to GRACoL7. Any measurement systems or CIP3 controller won't be affected by it, though you might have to adjust some of the CIP3 defaults.
As for the proofer. The Epson 9880 (and its smaller siblings 7880/4880) are perfect for 4c work and many spot color jobs as well. The new 7900/9900 are faster and more flexible with matte and photo black loaded simultanous and also the option to add a measurement device which can be fully software controlled. The 4.5.5 version of GMG ColorProof supports this inline device for calibrating, profiling and proof verification. So fully fool-proof unattended proofing is possible. A password protection in the software can even lock lower level users from changing critical hotfolder settings while still allowing to process jobs.
The ColorServer application is a real high end tool for color space conversion and processes images or complete PDFs. Separations, conversions, GCR-standardisation and even image resolution adjustments are done in a single step. Because of its internal structure it is faster than most ICC based applications (but can be switched to ICC mode if required) and GMG has over a dozen years of experience with device link profiles and if you read through the different threads of the forum users seem to like the results quite well.
ColorServer is also in use with many HP Indigo machines to have them match to CMYK press color spaces. Match quality is extremely close and for several print standards presets and profiles already exist.
One of the nice things with ColorServer: once you have a license you can add as many hotfolders as you like or need. So separation, CMYK space conversion, separation standardization, adjustment conversions to go from coated to uncoated stock and HP Indigo all can run on that single license.
Read through the threads what users think of these products. If you like what you read, you can in the US (and other American countries) contact
Jim.Summers@gmgcolor.com. If you're elsewhere contact
info@gmgcolor.com for info on local GMG subsidiaries or dealers where you can check out what I wrote.
Juergen