Buffer amp no gain

You are looking for a unity gain (i.e., voltage in = voltage out) buffer.

There are some tube buffers available such as one made by Tortuga and the two linked already in this thread but, as you pointed out, you do not need or want the volume control. I suspect it would be easy to construct the Pass B1 buffer without a volume control. It appears they still sell the board through the store. I suspect you would replace the VC with the correct value resistor, assuming you will operate it from the output of your current VC. I am not the one to help with that but I suspect it would be easy to do. This article may also be of some help.

@erik_squires You literally just described the reason preamps exist.

Yes, Erik has it right, the pre-amp can amplify the signal, it also attenuates the signal and sends a signal to the amp at the right impedance. I've never seen a top audio system without a preamp (some pretty good ones without but not state of the art systems).

The unity gain "buffer" that I like involves the use of transformers.  I've heard a few and liked how they remove hard and artificial sounding "edginess"  without sounding murky or dynamically dull.  The attached is a discussion of the subject:

I think Luxman, maybe among others, experimented with transformer based volume controls.   I have to say I've always been intrigued by using transformers either as volume controls or output buffers offering galvanic isolation and balanced outputs.

Erik,

The problem with most transformer volume controls was the limited number of volume steps—the right volume seemed to always be between adjacent steps.  The are some nice ones offered my MyEmia (autoformer) that has many steps and remotely controlled volume and balance.  They used to offer the autoformer and relay switching as a kit, so one could build the control into one’s own gear, but I think the kit days are long past.