Using Stereo Receivers as a headphone amp?

Hi guys. Today, at my local thrift store, I saw these 2 items there:

http://www.amazon.com/Onkyo-TX8511-TX-8511-Stereo-Receiver/dp/B00005T3WF/ref=sr_1_1?s=electronics&ie=UTF8&qid=1312699849&sr=1-1

http://www.topdjgear.com/denavprolog1.html

Right now, I'm running a foobar--> uDAC1 ---> Sennheiser HD600 configuration..... Would these represent considerable upgrades if I used the uDAC as a DAC, and then used one of these receivers as an amp for the headphones? .... Heck, is this even possible? 

If so, do I use the "phono" inputs on these stereo receivers to connect from my uDAC's RCA outputs? 

Sorry, I know I sound like a huge noob, but do you guys have any guidance you can give me on this subject?

Thanks!

Is there a way for me to know if there's a significant sound quality difference, or am I just gonna have to roll the dice completely? 

Quote:

Originally Posted by Uncle Erik 

Yes, give a receiver a try!

It'll also give you a way to run speakers if you want to.

Hey Uncle Erik! I've lurked a lot on these boards, and I've always enjoyed your posts. Very informative and down-to-earth. 

Are there any general rules for using stereo receivers as headphone amps? 

I know a lot of people said it's good to look for receivers from the 1970s or so... that the quality of their components were strong back then. However, these 2 receivers that I saw at my local thrift store are fairly new (in relative terms.... they're not from the 70s), I believe. Is there a big difference, if I'm using them as headphone amps?

Is there anything else I should look out for, in general,  in regards to stereo receivers?