Any Lambda would be a small incremental upgrade or a simple change of flavor but I'd hold out for a 007.
Something I just found in storage, my modified KingSound M-10:
Whole bass boost BS removed, RK27 installed instead, crap sand cast "plate" resistors replaced with Kiwame Carbon units, output caps upgraded and installed some heatsinks with some thermally conductive epoxy. Far better now but still not a good amplifier...