[velveteer]

How would the DAC in a Marantz SR6008 compare to, say, a Peachtree DacITx? Or a Schiit?
 
I ask because I'm currently running a Peachtree into a vintage Marantz 2285. With all the sales going on right now, it might be time to "modernize" my equipment...

 

[computerparts]

They usually cut a lot of corners in receiver dacs. Judging from the design of the others, I'd say they would all sound about the same.

 

[project86]

It varies wildly from one brand/model to the next. I had a Marantz SR7007 for a bit, it sounded pretty decent if not spectacular. Probably on par with the average $300-400 stand alone DAC if not the better examples in that bracket.
 
I tried an Onkyo NR929 briefly and it was not as good as the Marantz. Kind of soft and indistinct, like I'd expect from some $150 budget DAC. 
 
I've heard some Denon models sound decent and some sound very mediocre. It seems to change from year to year and is not necessarily tied to the price.
 
Now I'm using an Anthem and it's actually very good. The MRX 310/510/710 all have the same DACs, and they are very satisfying. I had to go all the way up to a Resonessence Labs Concero HD ($850 overachiever) to notice a clear benefit. 
 
I'd say upgrade for things like improved amplification section, or surround modes like DTS-HD/TrueHD, or room correction, but not necessarily just for the DAC function. 

 

[daerron]

I generally found the DACs in AVRs to be solid but unspectacular, though the Yamaha RX-A3010 sound pretty good using the Audiophilleo 2 USB SPDIF converter as a transport, but mid range DACs can easily do better.
 
Recently did a shootout in a friend's audio system between the Resonessence Concero, Peachtree DAC ITx and Emotiva XDA-2 and the Concero won by a long shot. The DAC ITx is not bad, but its a bit flat and uninteresting, while the XDA-2 lacks refinement, I'm surprised by the positive press it has received even at its low price point. The Concero is a great all round DAC and does very little wrong which is rare at the price. The Schiit Bifrost Uber is also worth looking into, but I haven't had the chance to listen to one yet.
 
If you want an AVR I would definitely follow Project86's advice and look at the Anthem line of receivers.