How old is too old for a Dac?

how do Schiit, Mytek and Berkeley make SQ from redbook CDs better?

is it upsampling??

or some innovative new circuit designs, or??

you should go to http://www.computeraudiophile.com/ and ask there

a lot of equip. designers and serious audiophiles that specialize in DACs and streaming are there 

there is a fair amount of recent research into noise injection

I am not clear on whether the engineers think that an optical of WiFi connection solves those problems or not

I'd bet you could find a new DAC that sounds better than one from ~~8 years ago even on redbook... the problem is to find one