Preamps without built in DAC silly question
Forgive me for posing such a silly question oh great and knowledgable ones:
I am considering picking up an Audio Research REF 5 SE. However, i do not see any digital inputs where i could go straight from my media PC to the pre-amp. Therefore i will have to keep using my Wyred DAC and connect to the AR 5SE via my balanced interconnects then out to my Levinson 331 Amp. If the DAC unit is doing the conversion already, why would one still want a pre-amp in-between the source signal and amplifier? What exactly is the pre-amp doing if it is not needed for the digital to analog conversion. Will the preamp "improve" the already converted signal? I know i must be missing something very obvious here so please enlighten me. If my logic is correct (which i doubt), the pre-amp would not make any sonic difference. Hence to really change my sound, wouldn't i need to also change my DAC? I think i'd be going backwards if i were to let my media PC do the DAC duty and send signals via RCA to the AR Ref5se. Lastly, besides making more products to sell, why would a pre-amp not include a DAC unit? I'm guessing its to keep prices down or keep things simple in the pre-amp? I look fwd to your replies.