AD conversion on a budget



I'm looking to improve upon the UNimpressive converters within my Digi001. Someone suggested to me that I look into getting an external wordclock since I can't really afford to by an 8 channel converter (like the apogee "rosetta"). Can someone please explain to me how clocking externally can audibly improve my rig during playback and record? At the moment I have a Presonus Digimax (8ch. mic pre) with an adat output that I use to get into Pro Tools to free up all the analog i/o's on the 001. I'll be upgrading to better preamps soon, but I'd like to learn more about this wordclock option before I do so. Someone please enlighten me. Rock!