Rob83 congrats on the new amp, and thanks for the review, especially the contrasts between the various pre-amps. That does help point that the XLS is quite transparent.
I have some old Sunfires (20, 22, 25 years) nearing retirement, and I might replace at least one of them (driving the JBL Atmos speakers) with XLS units. They would also be fine driving woofers. But for ESL panels, I'll add more Sanders ESL amps.
One unrelated observation from your picture: You can dramatically improve the sound from your system with two simple changes.
Put a rug on the floor in front of the speakers, have come right up to the base of the units.
Yes, the panel dispersion does not hit the floor but reflected energy and lower frequencies do bounce, so some minor absorption from the rug can help smooth things out and allow more direct energy to reach the listeners.
Place two absorbers behind the panels and the front wall. These can be DIY to look really nice, or you can buy commercial. They even sell ones with custom prints, just send them a pic of whatever design you'd like on them.
They should be >2" thick, with no reflective elements (no limp-mass sheet in them) and mounted so they are offset from the wall by 2 to 3" to improve low-end absorption.