Is the Manley Steelhead still relevant?

Lewm,

Thanks for the reply.  

I'm using the Steelhead's line in as a pre-amplifier for my DAC, which is then sent out to the amplifiers.  So, essentially the Steelhead line in does not add any gain, but a standard pre-amplifier would add some gain to the line in?  The only advantage to gain being additional signal, which could add to distortion?  

Thanks.

For your CD player or any other device that puts out what is generally considered a high output voltage, like a tape recorder, a television set audio output, etc., the gain added by a formal line stage is completely superfluous. The output voltage of your CD player is fully adequate to drive an amplifier.

@lewm 
Thanks for the detail.  I may try running my CD player without a pre-amplifier just to find out how it sounds.  (Unfortunately there's no volume control on my CD player, so I'll see how loud or soft it is.)  

So what you're essentially saying is that a pre-amplifier may be superfluous for CD players, and are essentially only volume control devices, which may also add some "color" to the signal?

the gain added by a formal line stage is completely superfluous.

What Lewm is referring to is the standard set by the industry back in the early 80's of 2V RMS for most source components. At the time, turntables were all but extinct. 
I disagree that a preamplifier is "superfluous". The better word would be, at best, "optional". 2V RMS is plenty for virtually every amplifier in terms of making full use of the amplifier's power. But for starters, what does that have to do with such features as input selection, balance, mute, phase inversion, etc? 
But more importantly, a great preamplifier does other things-it creates a sense of drive, propulsion, dynamics, and even space that is absent using a passive volume control at unity gain. Read any of John Atkinson's reviews of top tier preamplifiers over the last five years and he makes note of how he has come around to this realization after once thinking that a passive volume control offered a "purer signal". 

I was referring to GAIN only, when I wrote that a linestage is superfluous. Obviously it’s needed for attenuation (if the phono has no volume control) and for input selection, at a minimum. Sheesh!

I would not connect the full output of
a CDP direct to an amplifier. In certain cases you might damage your speakers.