Volume granularity in myspeak refers to the range of volume adjustments possible where you can hear a change in volume. With the pre90 and my CODA #8 and also my sold LSA Voyager 350 GAN the change in volume levels from the MUTE to MAX was limited. It was too loud over most of the volume settings. With the AHB2 stereo and mono this is not a problem and the volume can be adjusted from total MUTE to a very loud level. Each volume change had a noticeable affect on the loudness.
Unfortunately, my AHB2s are not the amps I use for the system that I want the pre90 to be used. I ended up buying the Benchmark LA4 for the AHB2's since I realized it was a better preamp. I had the HPA4 before but sold it when I got the Topping pre90. A little too fast to sell though I made money on the unit by selling it to Europe. The LA4 is amazing on the CODA #8 and the Voyager.
If you can get the pre90 to work it is a good unit.