Audio Research DACs

Audio Research usually doesn't mention much about their past line of products on their web page, so only current products are mentioned. I know ARC has the DAC3, DAC1, DAC5, with the DAC3 being the current version. Does anyone know the history of these DACs as far as sound, quality, etc. I am assuming DAC3 is the best since it's current, and as with DAC technology, USUALLY more recent is better...What would be the comparison between DAC3/DAC1/DAC5?