Awesome. I started building a toy C interpreter to the k5 spec (http://kparc.com/k.txt) based on the k4 data structures (http://kx.com/q/c/c/k.h) and documentation (http://code.kx.com/wiki/Cookbook/InterfacingWithC). That k2 manual is a good find.
Since you are playing in JS, you might also have a look at c.js (http://kx.com/q/c/c.js), which is the tool KX uses to translate between JS objects and k objects through web socket IPC with a k process (http://code.kx.com/wiki/Cookbook/Websocket). Might be useful to see how Arthur envisioned the k data structure in JS. Also, it would be kind of interesting to have a k5 process running in the browser talking with a k4 process running locally in the 32bit trial...