Not sure how a Canon workflow helps the OP who has an Epson 3880. I assume the Canon plugin would avoid the silent sRGB conversion by Photoshop on Windows.
The role of soft-proofing has been hotly debated recently elsewhere, especially that recent debate between C'tein in one corner and Andrew Rodney plus Mark H. McCormick-Goodhart in the other. I'm definitely in the pro-soft-proofing corner. No-one is saying that it isn't the print that counts, just that a fully functioning soft-proofing setup will get you there faster and with less waste. Not all jobs are well paying. YMMV.