I also run the ipod and Sirius direct to the amp via the headphone adapter and a set of RCA cables. I didn't want to punch more holes into the center console, so I mounted two wakeboard tower speakers to the t-top and it sounds great. Most also have adjustable tweeters so you can aim them at the drivers seat. If you don't have an ipod a cheap $30 flash drive MP3 player would work. They are solid state so there's no moving parts to get damaged from vibration.
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Bob