How old is too old for a Dac?

If it sounds good to you, than it is a good dac. 
I made the mistake of hearing an Audio Note DAC 3 Balanced and then nothing sounded good enough.

Dedicated CD transport without inner DAC will always sounds better that regular CD player when connected to the same DAC.From my personal experience regular CD players aren’t so good as transport.A dedicated CD transport doesn’t have analog circle and no inner DAC so capable to transfer a pure digital data to the DAC .

I agree that the newer DACs today are so good that there is almost no difference between red book CDs and "hi-res" .

Not to hijack, but I too am interested in upgrading my source, but honestly don't know where to start.  I have a Sony 5400es that has served me very well, but I don't know what I would have to spend on the used market on a dac to better it.  I have ARC gear, so was thinking an ARC dac would be logical, but with all this new stuff out, not sure what to do.  I'm sure at this point in time my 5400 can be bested on red book. I want balanced outputs, no more than ~2k new or used.  Can it be done? Or should I just stick with what I've got? 

ARC Reference dac is very expensive. The Schiit YGGORASIL is a good option on the 2k range price.

http://schiit.com/products/yggdrasil

Some guys of whatsthebest posted their lack of enthusiasm for the Yggy and other Schiit products compared to what’s available right now. Actually universally disliked. Might be worth a read.

http://www.whatsbestforum.com/showthread.php?19433-Chinese-DAC-shames-a-few-heavy-hitters/page11

YMMV. Best advice I’ve seen is to try before you buy.