First, if you want to do it well, you should look into a separate analog to digital converter (the opposite of a DAC).
MSB makes a couple. The MSB Pro (Model PAD-1) lists new for $799. The Audio Director (Model ADD-1) lists new for $599. I see used ones for sale from time to time. I think there is an Audiogon dealer who sells for 10% off list. Information is at www.msbtech.com
Sony makes a few models that are less costly. There are many models. The ones that come to mind are the PCM-701ES and SBM-1
Also check eBay under "Consumer Electronics:Home Audio & Video:Audio Components:Processors"