I have built only with the AMB regs with heatsinks, I closely watched temperatures and in comparison to Astro I’m running slightly cooler... and that’s without any heatsinking attached to the transistors.
I’m think directly soldering the regs to the board creates a thermal bottleneck.... ymmv
I stand corrected, my assumption came from the topology discussion here:
https://www.innerfidelity.com/content/lightning-quick-headamp-gs-x-mk2-headphone-amplifier
Thanks guys. After a read here and there I count myself more clueless than I originally was, I presumed the latest version was the SZ3 but as Spritzer says the serials are all over the shop and the SZ2 version I have may be new production.