I don't know if we know to much more about the currency, but I'll go through and look.
Boxings presumably come in at least two denominations (1-Boxing and 10-Boxing, the later are mentioned a handful of times). Technically they are called "imperials" boxing just being slang.
Clips are described as the smallest denomination of coin. Chapter 30 of TFE describes clips as being bronze, but they're described as copper in the WoA and HoA Ars Arcana, as well as a couple chapters of HoA.
...There really /isn't/ much there, is there? Anyway I totally like your idea about clips being clipped, it makes total sense.