Role of an Audio Receiver[SOLVED]

If it's a receiver, it also has a radio. 

There are very few DACs that work with an iPod.  DACs are generally used with computers, although anything digital has a DAC, such as an iPod or CD player.

My main headphone amp is a Realistic STA-2200 receiver from the early 70s.  It's big, it's massive, it has a lot of power, it sounds great, and it was dirt cheap, $25 plus $60 in shipping.  I took it to a recent meet because the entire line of HiFi Man orthos were going to be there and I wanted to hear them out of it.  HiFi Man also brought the EF-6, a  $1300 amp designed to drive the orthos.  The receiver was the equal of the EF-6 with the HE-6.

It really is only good for driving headphones that require a lot of power.  It's just too loud with easy to driver headphones.

Not all receivers are created equal though.  The STA-2200 was a top of the line receiver for it's time.  It was cheap because it was sold by Radio Shack.  TOTL 70s receivers from other brands can go for $500 - $1000 and up.

This thread talks a lot about using receivers as headphone amps http://www.head-fi.org/t/537704/calling-all-vintage-integrated-receiver-owners.

Edit:  The other thing revievers are good for is driving vintage eletrostatic or electet headphones.  My Stax Lambdas are driven by an transformer box connected to the speaker output.

I personally listen almost exclusively to digital music, mostly CDs that I've ripped, but some digital only music too.  I don't have much use for a CD player.  If I'm at my computer, I usually listen by shuffling albums in iTunes though my 4000+ album library. 

Almost all of my music is standard red book, 16bit, 44.1KHz.  I don't worry too much about hi rez stuff, especially since I don't hear the difference and very few people can, as long as the mastering is the same. 

If your computer is a PC, there can be numerous things that can make it sound different than an iPod.  Windows' sound system is not the best, your sound card may be doing strange things to the music, you can be picking up some EMF, etc.  In my experience, there should be little difference in sound from your PC and your iPod unless the PC has problems or inferior sound components.

Vintage receivers aren't hard to find, although they don't all work correctly and may need to be restored.  Not all of them sound great either, but that's true with modern amps too.  I've found some really good vintage receivers at Goodwill and other thrift stores.  I just take my iPod, a cable to connect it to the receiver inputs, and a pair of headphones and try them out.  I'd suggest that even for modern amps.

No, you don't need a preamp.