Hi direcow,
The 6th gen iPod (iPod Classic) is a different animal to the 4G and 5G/5.5G iMod.
With the 4G, 5G, and 5.5G iMod, we take the output directly off of the Wolfson dac chip and feed this to the output. There
is dc offset voltage on the L and R outputs from the Wolfson dac. It is important to block this before feeding into a headphone amp (or home audio preamp, or car stereo AUX jack or whatever). Not all electronics block this (and in the worst case, some have dc offset voltage at their input) and this can easily damage the dac chip in the iPod if there are no dc blocking caps to protect it.
With the 6G (iPod Classic), they are using a chip that incorporates the Cirrus dac and the output stage - all in one chip. There is no dc offset voltage, as they use a split supply to feed a section of this chip for the output stage. You do NOT need an iMod dock cable with the 6G (or any stock iPod for that matter) - you can use a standard line-out dock without the dc blocking caps.
The 4G iMod has the dc block caps inside the unit (the black gate caps) because we are able to make them fit and keep the signal path short. For the 5G/5.5G, ALO Audio makes the required iMod dock cable that has these caps installed in the dock plug. ALO also offers iMod dock units, which feature even high quality caps (Auricap, Vcap, Jensen) and in solid wood with high quality jacks, optional charging jack, etc...
Getting back to the 6G...just because the 6G does not need the caps does not mean it is a better sounding unit. Many who have compared the 6G to the 4G, 5G, and 5.5G iMods confirmed that the iMod comes out ahead in many areas... especially when you use the Auricap, Vcap, or Jensen cap dock with the 5g/5.5g iMod.
For those who decide not to use the iMod dock for the 5G/5.5G iMod (which has the dc blocking caps), that is your choice and if your dac fails, this is not in warranty and you will need to pay for a new motherboard and the costs to mod the iPod again. If your headphone amp amplifies the dc offset voltage and feeds this to your headphones, it is going to overheat the voice coils of the drivers. If that does not damage them and cause them to fail, at the very least it is NOT going to sound like the iMod because how can you expect your drivers to sound good if they are always being pushed in one direction (by the DC voltage) while trying to vibrate?
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So I'm guessing it's the split power supply in the 6/7G that helps prevent the dc offset from damaging equipment down the line?
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All of the stock iPods do NOT have dc offset voltage on their outputs. For example the 4G and 5G stock iPods have opamp output stages with dc blocking caps. They are not very good caps and I don't care for the sound of these output stages in the path (and removing that is what the iMod is all about). The 6G has a different output stage (built into the Cirrus CODEC chip) and again, there is no dc offset voltage. And the 7G is just like th 6G iPod Classic, but with a 120GB hard drive - unless there are other differences?
So ALL the stock iPods have no dc offset voltage. It is only with the 4G, 5G, and 5.5G iMod that this needs to be addressed. Again, in the case of the 4G, this is addressed inside of the unit. In the case of the 5G/5.5G, the ALO iMod dock cable (or wooden iMod dock) addresses it.
I hope this post helps clear things up!
Vinnie