How old is too old for a Dac?

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.

@andyz I know what you mean so happy about my AN dac-3 Signature now wondering how much better the Balanced might be? Happy for now, very happy, but good to know there's an upgrade path!