Just go DAT directly into the SPDIF input on your R44... Then copy the Card onto your PC... Easiest and most likely to give you a perfect copy of your DAT...
If you want to do your cassettes, then run your Tape Deck through the V3 into you R44... Use the V3 to adjust levels (if needed) and do the A>D Conversion... But you could just run the analog out of the Tape Deck into the analog in on the R44 and do the same thing (adjust levels and A>D)...
Terry