To have Emacs open .pxi files using clojure-mode, put the following into your ~/.emacs file:

(add-to-list 'auto-mode-alist '("\\.pxi\\'" . clojure-mode))

There is also a major mode for Pixie which provides some repl integration based on inf-clojure:

https://github.com/johnwalker/pixie-mode

in your .vimrc:

au BufNewFile,BufRead *.pxi set filetype=clojure