Are there passive attenuators that don't zero volume and only offer one input ?

Although the contributors seem very knowledgeable about passive control preamps I don't know if this is a good place to ask if the  Townsend passive Allegri Reference  preamp is the type of technology you understand and support and the type company and sound to consider replacing an ARC REF 10 preamp with the Allegri. I don't use a balance control, but have to have a remote, and only need an inbound balanced in and a balanced out. Is anyone up to speed on the Allegri reference and willing  to relate it's pros and cons to the other approaches you were describing, and then the replacement of an ARC 10 with it. If this question is too off base just say hello and move on Thanks.

±0.1VDC 1mVDC ripple is hardly anything to sneeze at.
Thyristors make gawdawful noise when switching. Pointless to control current in a device using a few mA.

No thyristors are ideal in this circuit as they exhibit much better complete switching. 

As you well know There are hundreds if not thousands of thyristors , each with different characteristics suiting different purpose, To which do you refer ?

The main advantage with thyristors  in rectifier circuits as you should know,  is to conduct current only in one direction,this suits when the load requires  DC. A diode in comparison always has a forward voltage droprelated to temperature so is always incomplete with its switching. In so doing it creates what is called dark current, also called reverse bias leakage current.  

With thyristors they too can exhibit forward voltage, however is related to the junction current,  With 3ma being the load that does just not occur, But if large current is the load seen by internal junctions then the thyristor does such transfer to exhibit forward voltage drop slowly.

Another major asset being that a thyristor is a  controlled device vs uncontrolled

Back to the topic, who agrees passives should be able to zero volume and have more than one input.

Back to the topic, who agrees passives should be able to zero volume and have more than one input.

These are trivial features and not important to me. What is important is that the passive preamp is well designed and gets out of the way. If in doing so it can zero volume and have more that one input fine, if not that is fine too.

As I stated previously I have had many passive preamps in my system. Some zero volume and have multiple inputs, some were made by manufacturers and some I DIYed. In the end the Lightspeed Attenuator which doesn't zero volume and has only one input is the one that I keep coming back to. One of the best bargains in audio and one of the best purchases I have ever made.

Not an issue to me.  I just had a passive built for me that purposely had only one input for purposes of SQ because it takes one switch out of the signal path.  If the volume doesn't go to zero then a mute switch would work fine.  I run mine in front of a unity-gain buffer and having remote control of volume, and an easy to read display, were more important to me.