Instead of hacking this yourself and getting it wrong, you might try setting up an lpd daemon to interact with the printer in between. Then you can use
without problems. Dot Matrix printers (as far as I know) never accepted HTML headers or PostScript (I found it amusing that you actually tried that :o). Depending on its age, it will use some obscure code that you won't find anywhere or on some Russian guy's web page who spent two years of his life reverse-engineering his printer (?). The only solution is to be happy with text or interact with the printer drivers in some manner. Also, you might even get to make an "older form of anti-aliased" text simply by using the drivers instead. lpd is the only thing that would make sense.... have fun.