Most of the iPod docks connect by analog out, especially for the older models. In that case you'd be limited by the DAC/opamp in the iPod. With BT you're limited to the SBC.

I think it's time to step back and look at what you really want to do, and what level quality you want. If you have all your audio files on a computer in high quality, I'd see how to get them directly to the receiver from there, without involving a portable media player, which I've never equated with quality--only convenience.
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Pioneer PDP-5020FD, Marantz SR6011
Axiom M5HP, VP160HP, QS8
Sony PS4, surround backs
-Chris