How does the sound of the PCC88 and PCC189 compare to the 6922/6DJ8 and its iterations?

The former are also classified as 7DJ8 tubes.

Check out the issue of Vacuum Tube Valley with the overview of the 6DJ8/6922. That would be much better than relying on the all-over-the-place anecdotal reports of different users! 

Upscale sells 7DJ8, why not ask them?
https://upscaleaudio.com/collections/preamp-tubes/products/matsushita-national-pcc88-7dj8

I'm not relying on all-over-the-place anecdotal reports of different users. I'm gathering information from all sources, sifting, evaluating and noting where there is consensus and divergence. Unfortunately the sample size of user experience is smaller than I had hoped.

Vacuum Tube Valley issue 7: the top three choices: Amperex 7308PQ (very dimensional and musical, with smooth balanced highs) - Siemens 6DJ8 (60's West German) - balanced sound, smooth and detailed. This tube does almost everything right. 10M Mullard (60's British) - natural and sweet sound with good balance. Minimal, if any sibilance. For those on a budget, the JAN/Philips 6DJ8 and 6922 are capable of good sound at a reasonable price.

I recommend getting a copy of Vacuum Tube Valley issue 7. They test and report on a wide variety of these frame-grid tubes! And are trustworthy! BTW, I have at least two preamps that use these tubes - an ARC SP6 and a Conrad Johnson PV3. Hence my interest.

Great reference. Thank you!

This is a good source of info: https://www.audioasylum.com/scripts/d.pl?audio/faq/joes-tubes.html

Alas, Joe has nothing to say about the tubes I'm inquiring about.

Sorry about that ! Brent Jesse Tubes lists and mentions them in the descriptions of tubes.  

FYI, I'm familiar with the readily available commentary, instead I'm interested in personal experience and comparisons.

The sound of a tube cannot be considered without context: it is dependent upon how it is employed in a circuit. One designer using the 7DJ8 to good effect is Tim De Paravicini, in his Ear-Yoshino 868 and 912 pre-amps.