Not sure which Epson or print driver you've been using to print CMYK files. For most, if not all of the Epson printers I've used, the last thing one would want to do is send the printer a CMYK file. The Epson printer needs to receive an RGB file, which it then converts to CMYK for printing. If you send a CMYK file the printer software will attempt to convert it to RGB and then back to CMYK. All of this to say that the end result is almost always pretty ugly looking. I assume the reason for the 8K$ Rip is to do all of that work upfront so that the Epson printer can handle the file and produce the desired results. I print quite a variety of subject matter and from various file formats. Whatever the file format that's presented to me I convert it to TIFF in Photoshop. Do to the volume of work, most of my printing is done in PS as well. So far I've found Lightroom somewhat slow compared to PS for my printing requirements, but that may change as I become more familiar with all of the nuances in LR. Most of the printing I do is for other photogs and I also do fine art reproduction for local artists, an area that is expanding nicely. I print on Photo papers(SemiGloss, Luster and occasionally Gloss) as well as heavy weight Fine Art paper, mostly Epson Cold Press Natural. I also print canvas, using Breathing Color Chromata White. I use an Epson 9900 and also an older 7600 for smaller jobs that don't require quite the precision I can obtain with the 9900. The 7600 is set up with Matte Black ink for the Fine Art paper. On the 9900 the cost of changing from PK to MK and back is approximately $13.00, so of course I always want to be doing more that one Matte Black print in order to do the switch to MK.
Of course to reiterate some of what Jim wrote, display calibration and good printer profiles are the basis for successful printing on any platform. For the 9900 I find the canned profiles(the ones loaded with the driver) do a fine job, but you can also have custom profiles made or do them yourself. I hope this is of some help.
Gary