Ipod to stereo amplifer: getting volume


I have quite powerful higher end stereo amplifer that accepts
signals from most of the usual input sources. We tried connecting
an Ipod output to the stereo at a party to discover we could not
get much volume. Not sure if this is resistivity issue or maybe
the Ipod needs a pre-amp, but I am guessing there are people
here who immediately recognize this problem and know how this
is generally solved. If there exists a commercial pre-amp, for
instance that would be nice to hear about.

Thanks in advance!

Dominic

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