The answer to your question is in the back of the SV3800 (I have an SV3700, but I assume the answer is the same). There are a series of DIP switches in the back. One of them (I believe it's the one that's farthest to the left) selects either the analog input or the digital input.
Of course, in either case, the only way you can pass the incoming signal on to your analog preamp or amplifier is to put the DAT into record mode.
Of course, in either case, the only way you can pass the incoming signal on to your analog preamp or amplifier is to put the DAT into record mode.