Pre amp with Dac

The Mytek is a great suggestion. 

The Ayre Codex can be run as a DAC with Preamp Volume function.
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I have the C510 (same internals as M51) and would say it's very detailed & doesn't have any glaring faults.  I recently auditioned the Codex and found it just a little bit better all around (but not enough to feel it was worth the price to upgrade).  The following week I heard the Chord Hugo2 and that just seemed to do everything right. Saving my money for one now.

If you want to save some money for other parts of your setup, The Emotiva Stealth DC-1 gets really good reviews. It comes with a remote, one set of RCA inputs, a Balanced DAC, and a great headphone amp.

is having the DAC inside your preamp a must as you really are losing out on many great used Preamps and DAC as separates. having an outboard DAC also lets you upgrade the DAC down the road.  DAC's Are getting smaller by the year and could easily be placed behind another component if you don't want to see it.