FYI- if you drilled holes in the boxes, that may void the warranty- manufacturers don't like ANY alterations. Someone opn Facebook was asking about doing that and I mentioned the warranty status issue and people who have never worked in audio gave me a hard time about it. After 45+ years in the business, I wouldn't recommend that as long as they're never operated at the maximum power or cranked with amplifiers that struggle at high output. Not saying you will, but things happen. If the warranty coverage involves user-replacement of drivers, it won't be an issue.
A friend is one of KEF's regional sales managers- I'm going to suggest that threaded inserts be added to the smaller speakers, but I don't know if the company will be receptive. They're very British, you know.