Sb, - I think I may have observed something similar....
On a couple of Police tracks it did seem as though the bass drum was quieter, until I realized that the image had deepened considerably and the bass drum was now further towards the rear of the image with the rest of the drum kit and as such not as loud as before, but the dynamics were still crisp.
On Eric Clapton's Unplugged album there was always quite a loud thumping of his foot on the stage. But as I moved up through the Harmony line this became much less annoying and is now in the background, but the overall bass performance improved and is now much tighter, so I figure it's now where the engineer intended it to be - it sounds more natural.
So as a result of the effect these RCA's seem to have on the image, I now listen in 3D - by that I mean that whenever I observe a change that seems a little "alien" to what my ears are accustomed too, I focus on the image to determine if the changes I am hearing are due to a change in an instrument's placement within the image.
Regards.