@benzman - not sure which version of the microzotl pre you had, but mine has - 15db and - 30db gain adjustments. Sweet spot for me is the 15db gain setting. With that I can bring the volume up o 50 out of 99 no problem. I sit about 7 ft away from the speakers and listen at about 55 to 65 db.
I don’t have an apples to apples comparison but I was able to borrow the rhumba extreme 1.3 for a week driving schiit aegir monoblocks. I was really impressed by the increased micro dynamics. It also threw a taller and wider stage than my Pass integrated. On the downside, I could not live with the volume control. Just not enough useful range and I was never able to get past 10 o’clock on the dial.
No, they’re absolutely not a lateral move. They’re a “different” move, but whether that’s better or worse depends on what the OP is looking for sonically. That’s the absolute key.
I agree with @jasonbourne52. The EAR 868 is well regarded. The preamps you listed are likely a lateral move. If you want to take it up a notch, consider Audio Research REF 5SE... supposedly ARC pre's pair well with PASS amps.
From what I’ve read I’d guess the LTA and Backert might sound a little less rich and add more upper-end detail — a little more white wine or Rosé and a little less red wine. But that’s just a guess. Member Terry London reviewed both the LTA and Backert (not sure if it was the Extreme model) I think for Stereo Times and slightly preferred the LTA, but it was pretty close as I recall and doubt you could go wrong with either if they deliver sound qualities and/or improvements you might be looking for. Then again, you’ve obviously got a great preamp so read the reviews and make sure you’re not actually going backwards from where you are. FWIW, and best of luck.