Does remote control degrade the sound of tube preamps?

Great question.

For decades, meters or displays would be included in high end equipment, with the ability to defeat them. In the last few years Audio Research took the problem head on. They decided, if they were to have “silent” meters they would have to design and manufacture their own… ones that did not impact the sound (ghost meters). Before this audio companies just purchased generic meters… and they interfered with the sound quality.

This is how the high end moves forward. As a manufacturer you can choose the cheapest parts to make a piece of gear (this is how we got $20 Blu-ray players), or chose the very best component for a given design. Then, when it counts… make your own… think Focal… making their own drivers.

In theory anything you put in the signal path will alter the sound (usually negatively)

https://tortugaaudio.com/docs/ldr-volume-control2/

Turtaga Audio makes an optical based attenuator that doesn't effect the signal path.

or

The Hornehoppe 

The Truth passive preamp. 

http://www.thehornshoppe.com/the_truth_pre_amp.html

There is nothing that makes remote controlled volume control inferior in sound quality.  If it is implemented with a motorized potentiometer, the quality is entirely dependent on the quality of the potentiometer, not on the motor whose only job is to twist the shaft just as your hand would also do.  Even if your volume control is a rotary step attenuator, it is possible to physically move the dial under motor control (Ayre does this).  Many very good attenuators are ladder step attenuators that are switched by relays, and the relays are always remote controllable.

It is so important to get volume set just right to get optimum sound quality and satisfaction, and that can only be done practically by remote control as you sit in the sweet spot and instantaneously hear the result.  Remote control of volume is pretty much an essential feature, not merely a convenience.  Without it, one tends to just live with something close to the right volume instead of actually determining what is the right volume.

There have been greatsounding preamps that use a remote cj uses relays and switches in individual resistors

Ken Steven’s makes an awesome preamp but his heart is not into convenience 

+1 @larryi