If your home theatre already has an preamp (source selection and tone controls) and a power amplifier, then what you want is an HD FM tuner (one component), and an IPod module for your existing preamp.
When you say a "receiver", that typically means a single unit with multiple inputs, a preamplifier section, a power amplifier, and speaker outputs.
Depending on how old your existing home theater set up is, the best thing for you may be to get a good home theater receiver, which should offer multiple HDMI inputs for sources like a Cable/Sat/Fios/DirectTV, bluray disc player, game console, HTPC, and iPod, as well as a built-in AM FM HD tuner, and outputs for 7.1 speakers and HDMI to your display(s).