The Stovebolt Site Forums The Shop Area The Electrical Bay The Radio Bench Would this work for I-tunes

You should check out this link http://www.metroccca.org/tech_articles/tech_08_summer.pdf
It is all about 6 VOLT CONVERTERS for classic or antique automobiles.
Here is a link to one of the converters reviewed. http://www.6to12volt.com/
The above converters can handle more amperage. But cost more.
The converter that you mentioned is really designed to just power radio/CD head units.
Looks like Sony makes an amp that runs on 6 volts link http://www.thesamba.com/vw/classifieds/detail.php?id=796241

After weighting the pros and cons your probably better off buying a 12 volt battery put behind the seat and trickle charge it once in a while.
Its cheaper.