So, I think this is sort of an apples and oranges comparison. The two amps will sound very different.
Your speakers present a very challenging load in the bass region, with both low impedance and the electrical phase angle. There is little doubt that your XA100.8s are currently running out of steam there. Take a look even at the other Pass Class A amp reviews and tests, you will see that even the XA200.8s are not the last word in bass control and drive with a challenging speaker like the Sasha.
However, the mids and highs with the Pass are to die for, in the view of some (me included). What you ultimately give up is bass control and slam, again when driving a challenging speaker like the Sasha. Or, my own Focal Scala Utopia Evo.
If you go to the Agostino Progression monoblocks you will get tight bass that is unbelievably controlled, and you will probably be impressed at what your excellent speakers are capable of. But the Progressions are Class AB, so you will not have that pure Class A sound. There is a cost for the dynamics and such, and no amp is perfect.
So it really depends what you want, and what is important to you. You could try to have it both ways and get a Pass X600.8, which is more than equal to the Progressions, and has like 50 watts Class A into 8 ohms, and maybe like 100 watts into 4. They sound great, but these are really hard to find used however. I have looked.
I was confronted with a very similar scenario, with my Scala Utopia Evo. I loved the sound driving with a Pass XA160.8, it was heavenly. But the Scala's also present a very challenging load in the bass region, with both low impedance and the electrical phase angle, like your Sasha's. I wasn't getting everything in the bottom I knew was there.
However, after having them a year I realized that I had forgotten that they were able to be bi-amped. I took off the jumpers and let the mid/tweets run on the XA160.8s. I still had my previous amps, Pass X600.5s, which are like 600 watts into 8 and 1200 watts into 4 ohms. I put those on the bottom driving the woofers. They have the same gain, match perfectly. Desmond was very helpful of course, and this is what I am running right now.
It's total nirvana. Astoundingly tight and deep bass, that I can't believe the Scala's were even capable of. The mids and highs, totally separate and driven with the XA160.8 under no stress sounds incredible. I went and relistened to all my old standards and was blown away. It's just nuts good.
The only issue is I am now running two rather large monoblocks per side, and the whole thing eats like 900 watts a side. But I am happy as hell with the sound and don't see how I can improve it at this point.
I hope this helps you understand where you are and what your contemplated amplifier change would do. It's up to you and depends on what you like. If you like the Pass sound, as I do also, you may want to find a X600.5 or better a X600.8 to run the Sasha's and get closer to what you are hearing now.