Timru's suggestion of the Mediabridge mini to RCA connector from headphone out is certainly easy. Not that much harder but possibly providing a step up in sound quality for not a lot of money would be to add something like an AudioQuest Dragonfly DAC on a USB port of your Laptop. USB>>AudioQuest Dragonfly DAC>>Mediabridge mini to RCAs IC>>Preamp. A low cost/high value product to consider using with the above is BitPerfect ($10?; software to run your iTunes music).
