Given the form factor of the amplifier, it may be difficult to upgrade to another amplifier module (e.g. Purifi, as you mentioned). The overall build looks pretty compact, so a different amplifier module just might not fit. To find something that works, you may not necessarily get the latest state-of-art class-D amplifier modules. If there is an input buffer that is separate from the amplifier module, it may change the gain structure of the amplifier. Additionally, the power supply would have to meet the same specs for the new amplifier module.
Alternatively, class A/B chip amp modules do sound great and could be an upgrade option (at lower power), but I would be concerned about having an underspec'd power supply and cooling thermal issues on the amplifier chip.
I actually look at this differently than you. I think that it would more sacrilege to modify the amp to chase the latest class-D trends. If you keep it and it collects dust, you still may find a way to use it down the road. Otherwise, selling it - especially on Audiocircle with the GR Research circle - would get it in someone's hands that understands the pedigree of amp and values Gary's work. I don't think that is sacrilege.
