Can Burr-Brown OPA627 DIFET Op amps...

Here's a couple places they can be purchased:

http://www.referenceaudiomods.com/Merchant2/merchant.mvc?store_code=RAM&screen=PROD&product_code=AC_OPA627

http://www.futurlec.com/ICLinearOpAmps1.shtml

You might need these too:

http://www.cimarrontechnology.com/index.asp?PageAction=VIEWPROD&ProdID=9

My guess is some older DACs can use them, and some can't...