Do I really need a preamp?

In this particular case, given the relatively low output impedance of the DAC2 series, and given the 32 bit processing that is utilized in the digital part of its "hybrid gain control" mechanism, and provided that none of your sources are phono cartridge/phono stage combinations providing particularly low output (gain does not appear to be specified for the analog inputs of those DAC2 models which provide analog inputs), you don't "need" a preamp, at least from a technical standpoint.

As many of the others have indicated, though, whether or not you would find incorporating a preamp in the signal path to be sonically preferable is not predictable with any certainty, as it is system dependent, listener dependent, and perhaps even recording dependent. It might even be dependent (in unpredictable ways) on whether or not the power amp you settle on would be driven by the DAC2's balanced or unbalanced outputs.

Personally, my instinct is to place the burden of proof on adding anything to the signal path that might not be necessary. And my suspicion is that while a high quality active preamp, especially one that is tube-based, would more likely than not enhance the sound quality of your system, obtaining that enhancement to a meaningful degree, and without introducing unwanted side-effects, is likely to cost significantly more than the sub-$2K price you will be paying for the DAC2 itself.

Good luck, however you decide to proceed. Regards,
-- Al

I have generally found that a good active, well matched preamp can provide the drive a amplifier needs to show off its capabilities, not to mention you have the ability to switch between sources.

For an exception and laughs I purchased a Lepai Class D integrated amp (can be held in the palm of your hand) rated at 100 watts per channel, it uses a passive preamp and costs just over one hundred dollars new. After 400 hours of break-in it was astonishing how good it sounded and transformed itself. I thought it compared very well to some far more expensive components I own and I'm no longer laughing.

It is then 95% possible that the Benchmark DAC2 can be all you need, bypassing the preamp all together.

In terms of gain you don't need one. And having no preamp will make your stereo sound more lively but only a touch. What a tube preamp does really well amongst other things is allow you to voice your system. If your speakers have a benign impedance curve (if they're 8ohms nominal they probably do) the linestage in your preamp will have the greatest influence on the overall sound which is really handy; you can swap out relatively inexpensive nos tubes instead of endlessly buying new speakers, amps or sources trying to get the sound you're after. I try to get everything as neutral as possible apart from the preamp's linestage. So yeah, chalk me up one vote for a tube pre.

In terms of gain you don't need one. And having no preamp will make your stereo sound more lively but only a touch. What a tube preamp does really well amongst other things is allow you to voice your system. If your speakers have a benign impedance curve (if they're 8ohms nominal they probably do) the linestage in your preamp will have the greatest influence on the overall sound which is really handy; you can swap out relatively inexpensive nos tubes instead of endlessly buying new speakers, amps or sources trying to get the sound you're after. I try to get everything as neutral as possible apart from the preamp's linestage. So yeah, chalk me up one vote for a tube pre.

How can a preamp better the input signal from a DAC or anything else? Wouldn't this be classified as "Coloration" since it must alter the original sound to be "Better?" Of course better is in the ears of the beholder.
I use a Benchmark DAC 2 HGC running balanced Audioquest Sky cables.
I also have another pair of Sky so I could experiment with this very thing.
I think going through an extra set of interconnects affects the sound in and of itself. My reference is taking the DAC straight into an Aesthetix Atlas driving a pair of Vandersteen Quatro CT's. I have tried the ARC REF 5 (my normal preamp before this computer audio experiment) and there's a slight decrease in resolution with a slight added tube coloration when it is in the loop. Some would probably call this better sound but it is a definite coloration to me. Guess you go with your own ears but just my take.