Is Pre-Amp needed

 THEIR source’s preamp

???  Sorry there's no such thing!
The output buffer in the source is the same if it has a digital domain volume control or not. And only if that volume control goes below 75% of full does it start to "bit strip". 
Many hiend source counter this by have a gain setting for the buffer stage, so then the digital volume control can be used at or above 75%. And if you have one that doesn't have the buffer gain setting or digital volume control the the answer is to leave it at full up and use an external passive volume control.

I have a $11k retail DAC which has a very nice analog output stage and volume control. It sounds really nice amp direct. It sounds even better through an Audio Research Reference preamp. YMMV.

If that's the case then you don't like the sound of your source direct, and need to colour it with the AR preamp's colorations and distortions. 

Cheers George  

George, your absolute assertions are not absolute for all equipment. The ARC preamp provides more of everything, especially the layering of instruments. Put a great preamp in your system and see for yourself. If you dont like it then you have only established one data point, yours, not an absolute.

I used to own a dual mono TVC which I sold. The new owner claims that it bested a $12k Bespoke TVC. A TVC is a step-down attenuator, is what I understand. So the signal from source is toned down before being sent to the power amp.
I was pretty happy with the TVC for years. But when I replaced this TVC with an active preamp, the system gained musicality and life. There is a certain fullness that makes listening more pleasurable. Bass is rock solid and startling at times. I am amazed by what a great active preamp can bring to your system. And I had avoided an active preamp for 9 years thinking that they would distort or add fuzziness to the original sound from the source. Well, lesson learned!

The ARC preamp provides more of everything, especially the layering of instruments.

It can’t make something from nothing, all it can do is to add colouration/distortion euphonics if you wish to call it that. If it’s not on the recording a preamp cannot make it. There is no voodoo in hifi!

I was pretty happy with the TVC for years. But when I replaced this TVC with an active preamp, the system gained musicality and life.

TVC's are a "transformer based volume control" your lucky that's all you disliked about them.

Cheers George