Best Preamp - NO preamp... (?)

Mitch2, thank you for taking the time to explain in detail the other variables involved and pointing out the genius behind Steve McCormacks designs which I believe are top notch!

Thanks for the detailed post Mitch.
I totally agree with you that if your source and amp gain and/or impedance are mismatched, an active unit may improve the overall result.
What i'm questioning is the common approach on how to solve this mismatch.
My suggestion is that you might be better off trying to find a better matched source-amp combination than introducing an active pre-amp to make them work well together. 
If you invest the money you save on the preamp, and get an upgraded and better matched source or amp, the overall result may be much better than having to introduce a preamp as a 'match maker' for a 'given' source and amp.

I would like to add a quote from Ted Smith that addresses cable capacitance as well, which was posted on the PS Audio forum regarding the DS DAC direct to amp approach. The key sentence here IMHO is

• "We don’t always build our systems from whole cloth where we might have the opportunity to find a set of components with no interface issues: a preamp is a good thing to have on hand for the cases where other factors like gain mismatch or cable length or… get in the way of a well balanced system." - 
  

So why not strive for a well balanced, preamp-less system to begin with?

Here is the full quote:

“There are two issues that come to mind: gain (which has already been mentioned) and the other is cable capacitance.

With respect to gain, there’s a “best” sensitivity of amp to use with the DS direct: you need enough headroom to have dynamic music (even on your louder tracks) but also enough sensitivity that you aren’t using the volume control far from 100 a lot of the time. Obviously if your music collection has tracks that are significantly different in loudness or dynamic range or if the amp isn’t sensitive enough or is way too sensitive you’ll probably want a preamp.
With cables that have too high of a capacitance there are FR response issues with almost any source. With most sources high capacitance implies a high frequency rolloff, but at times the transformer output of the DS can interact with cable capacitance to add a little high frequency boost. In an already existent system that already has high capacitance cables but is otherwise balanced changing from some other DAC to a DS may make quite a difference in the very top of the audio band. Either a rolloff or a boost of the highs could be beneficial in some setups, but in general, average to lower capacitance cables will be better with the DS or you’ll need a preamp to drive/buffer a higher capacitance or long run cables after the DS.
My counter argument to the minimalist point of view is that “Why should you expect a $6000 preamp in a $6000 DAC for free?” We don’t always build our systems from whole cloth where we might have the opportunity to find a set of components with no interface issues: a preamp is a good thing to have on hand for the cases where other factors like gain mismatch or cable length or… get in the way of a well balanced system.
Given a particular amp the DS could be designed so that you probably wouldn’t want a preamp – and similarly given the DS an amp could be designed so you probably don’t want a preamp, but in real life, as all things in audiophile land, you’ll need to listen for yourself to different setups and make up your own mind.”

If your source has sufficient output voltage, there are a couple of DACs that offer volume control solutions that maybe superior to even properly implemented passives, and may approach the sonic quality of very good active preamps.  These are implemented by changing the reference voltage of the dacs, which does not affect the "bits."

Steve Nugent's Empirical Audio Overdrive SE and SX offer this type of on-board volume control method as does Metrum's new Adagio.  I am currently enjoying Metrum's Pavane (which does not offer volume control) but I am very curious to try the Adagio, which is said to offer other sonic improvements over the already very good Pavane, in addition to the volume control option.

I have no clear idea how PS Audio's DirectStream DAC controls volume although it is said to be in the "digital domain."  It was surprising to me that Art Dudley didn't even try the direct-to-amp approach in  Stereophile's first review of the DirectStream DAC.  He brushed it off by saying;

Given the choice, I always prefer the sound of my system with an active preamplifier—the passive approach seems to me sorely lacking in drive by comparison—so I didn't try using the DirectStream to directly drive any of my amps.

Robert Deutsch did try it direct and had this to say in his 2015 follow-up;

Since the DS's analog output is variable, it can be used to drive an amplifier directly rather than running the signal through a preamp. Like most people who've compared a high-quality active preamp with a passive controller, I've found active preamps to be superior, particularly in dynamics. But the DS is different: its output level is controlled in the digital, not the analog domain, and Ted Smith, lead designer of the DS, claims that using the DS's variable output to drive an amp directly results in no loss of resolution. In fact, this is what PSA recommends for optimal sound quality.

Listening at matched levels through my Convergent Audio Technology SL-1 Renaissance preamp vs direct connection, I went back and forth at least a half-dozen times, trying to decide which was better—which should give you an idea of how close the sounds were. The sound through the CAT was a bit warmer, which was welcome with voices. The direct connection to the MC275LE resulted in even more finely defined detail, but perhaps veered slightly in the "clinical" direction. Overall, I preferred the connection through the preamp, but it was a close thing. The CAT is one of the best preamps around; pitted against a lesser preamp, the direct connection would likely be the winner.

He seemed to observe the "more detailed but thinner, dryer, less full, etc." perception that others report when running DACs direct to amplifiers, or when using passives, compared to using active preamps.  In fairness to PS Audio, AudioStream also preferred having an Ayre preamp in the signal path when compared to running the Empirical Audio Overdrive SE direct to their Ayre amplifiers.

Here is a part of the review from 6 Moons for the new Gryphon Antileon Evo poweramp, driving Wilson Alexia’s
What was used first as the preamp was his Supratek Reference DHT, and yes this quote of part of the review is pushing my product, but it goes to show at least to this reviewer what a passive can do.
And if his source (AMR CD-77.1) had a volume control of it’s own, it would have sounded even better to him direct.

That’s the quintessential description for the sound of the Antileon EVO, too. There’s a sense of weight, power, dominance and uncompromising authority to music when played via this amplifier. And it’s not just about the bass either. It’s about overall dynamics that approach reality (yes, rest of gear permitting…) with explosive contrasts. This last came through even more outwardly when I connected George Stantscheff’s Lightspeed Attenuator quad-matched LDR passive. The Lightspeed does no harm. It’s as clear a conduit to the musical content from your source as you’re going to get, provided all impedance parameters are optimal, and without hindering dynamic expression in any way, shape or form.

Cheers George

Hi George,
I'm very impressed with your candor:

And if his source (AMR CD-77.1) had a volume control of it’s own, it would have sounded even better to him direct.

Wow... coming from the manufacturer of the product, that is rare.
If I ever consider a passive again, (for this system or another one) your Lightspeed attenuator will be the first one I'll try.