I'll share with you what I use for optimal output on my PC-600. First off forget all that "print everything in spot color" stuff, I get my best results printing CMY process for most colors. The only time I prefer to print spot color is when I'm just printing black. Next important thing is I only use Roland ribbons, everything else is crap.
I run my PC-600 on Flexi Pro 6.6, I tried everthing else and found that Flexi gives you much more control over your output. In Flexi's Production Manager you'll want to change the Rendering Intent default setting to Spot Color for Vector Graphics and Relative Colormeteric for Bitmap Images. I found I got better print results from Roland's output profiles than the profiles in Flexi, can't seem to find them on Roland's site even though I know they are there somewhere. I've got them and I'll e-mail them to you. You don't really ever need to print at 1200 DPI, 600 DPI is fine for most everything. I also suggest you design your artwork in CMYK, I use a CMYK color palette downloaded from Trumatch, it has 50 basic colors which you can print out a vinyl color sample and design from that, adjust any colors as needed. I have that loaded into a Flexi swatch table which I can also send you, it also contains the Roland spot color swatches from Flexi's color library (see attached sample), just put it in your swatch folder and then load it. That should get you going, shoot me your e-mail address in a PM so I can send the files.