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.
chenglo1

The audio research DSPre ha a built in DAC. Personally I would never buy one. I don't want to have to change my preamp if I want to upgrade my DAC.

The preamp is the control center of your system. A volume control on a DAC just can't compare to a truly great preamp.

I would suggest you borrow a Ref 5se from your dealer and listen to it in your system. Try it both ways and see which way you prefer. That is the only way that you will know for sure.
Reasons to use a pre-amp:

1) you always need a volume control somewhere and no volume control otherwise
2) you may need to switch between multiple inputs
3)pre-amps tend to impart a particular sound quality that one might like. This is more of value when you have multiple sources and you want them to sound more similar.
4) there may be other useful features in teh pre-amp like balance and tone controls among others.

That's pretty much it. Pre-amps are optional in more cases these days especially if one has a single digital source with a decent volume control already.
Mapman pretty much nailed it. If you do not need input switching, a DAC with a very good volume attenuator is probably the cleanest, most honest sound you'll get out of that source.

If your Wyred DAC - you did not state the model - has a good volume control, I'd say give it a whirl direct-connected, you may be pleasantly surprised!

-RW-