Never technically been in stirrups but I visited a play enema Domme 15 years ago for enemas and the second visit she hung my ankles in stirrup-like restraints to give me the first enema. It was extremely submissive and erotic. I'd love to do it again. The next two enemas on the same day were very fun as well, one on all fours followed by a full JBL bag, but the stirrup enema was terrific.
One of my favorite enema scenes is in a fiction story I first read 10-15 years ago, and fortunately I now own a copy. It's really a rubber fetish story about a young English Domme who kidnaps her old school friend and turns her into her rubber sex slave. However, after dressing her completely in rubber, including hood, gloves and gas mask, she sits her in a GYN type stirrup chair and straps her into it. After giving her a fingered G-spot orgasm "to relax her" she installs a rubber bladder catheter and drainage bag and then a wide enema nozzle/speculum which the sub girl says feels like she "pushed it in forever." Then the girl looks above her head to see a huge bulging enema bag and they start to fill her up while she can't move in the stirrups. Her descriptions of what the 4-5 Q enema feel like while in stirrups are wonderful, and the result is that she has a huge spontaneous orgasm while "all that water was whooshing out of me" down the drainage tube. One of the most erotic stories I've ever read, but then I also have an intense rubber kink.