Depends on what you're sourcing from. Does your source have a line level analog output? If yes, then you're fine. If not, then yes you need a DAC. Remember that a lot of devices have DACs built into them (like CD players, computers, etc).
which amp and amps only run on analogue signal so if your trying to feed an amp a digital signal then yes your going to need a d/ac like you cant plug a SPDIF or a optical cable into a amp and hope it works. where as you can plug any line level or phono into the amp and it should work to some extent.
You can't run a raw (as in un-equalized/pre-amp'd) phono line into a line sink; it'll be overly bright and won't have enough gain. See: http://en.wikipedia.org/wiki/RIAA_curve