Too many DIY choices, advice appreciated.

Hey all. I've read heaps of stuff here but now I am finally dipping my feet in the DIY DAC area, I would love some advice. I'm an Aussie in the south of Brazil and I'm looking for a cheap sub US$50 kit with coax and/or S/PDIF in (with PS if possible). I'm happy and qualified to solder but being here in Brazil and far from support, I'd be more comfortable with an assembled board that I only need to fit in a box and go but this is not a deal breaker. There are just so dam many chip choices with these kits and I am hoping someone out there can give me some direction. I've researched the crap out of the choices and have actually disappeared up my own *** with confusion. :confused: Please take a look at my system below and give me an idea of what may sound good with it.
My system is a good top end ASUS mobo PC built and specd myself. I am using an old but sweet Marantz PM 300 with a pair of Tannoy Eclipses and a another pair of Electro-Voice IIs. All my CDs are in flac format but I still have a shitload of 320 MP3s that I sometimes play as well. Thanks in advance all, Ward