How do I connect Benchmark DAC

Very simple. CD digital out (via RCA coax or Toslink) into the Benchmark DAC (using RCA or BNC terminated cable, or Toslink). Then RCA analog outs from Benchmark into the CD input of your Pre (or another aux input, if you still want to use CD direct to Pre). Flip the (rear) toggle switch of the Benchmark to FIXED volume out, so all volume control is via the Pre.

Assuming that you have digital out from your CDP (otherwise, the DAC would unfortunately be of no use), you would connect a digital cable from the digital out of the CDP to digital in on the DAC, then analog out from the DAC to any line level input on the pre.

You need 75ohm digital coax RCA-to-BNC cable like this:
www.amazon

This cable should be either very short (< 1ft) or at least 1.5m (there are technical reasons for that). Select coax switch position on the front panel of DAC1.

Benchmark DAC1 has two sets of outputs RCA or XLR. If your preamp or amp has already XLR inputs - get XLR interconnect. Otherwise use RCA outputs.

There is small switch on the back of DAC1. It allows to choose Calibrated-Off-Variable output. Use "Calibrated" when connecting to preamp with volume control, Variable when connecting directly to power amp (using DAC1 volume control) or "Off" when you listen on the headphones.

In Calibrated mode two 10-turn trimpots marked L and R allow to fine trim output levels. Adjust them if you have to.

If you decide to connect your DAC1 directly to power amp (as I did) select "Variable" position and protect switch from accidental change (I inserted piece of plastic into the hole) since it will put max level directly to power amp in "Calibrated" position.