Seeking advise on 6922 tubes for a preamplifier..

Different tubes produce different tonal patterns in different equipment. Much depends on the design of your pre-amp and your sonic expectations. If you identify your pre-amp and tell us what you are trying to improve in its sound quality it would be more meaningful. It helps a whole lot if the person making the recommendation has experience with your pre-amp and knows what aspect(s) you feel it is important to improve by making tube changes.

Usa, Think of changing tubes as comparible to changing components. It can make as much or more difference than the differences between CDP's or amps.

Lacking specific knowledge of the outcome of changing tubes in the '16' and what if any tonal differences you may appreciate, what I would suggest is that you do a bit of experimenting with some new production tubes to see what differences they might make. For example if you find that either JJ's, EI's, EH's, all of which have a different sonic signature, float you boat, you will have a basis for looking for some better NOS version with the same tonal signature, but might improve on things like high frequency clarity, bass response, etc.

Hope that helps a bit.