I asked Bobby about the impedance boxes awhile back and he said I didn't need them.
Speltz/Atma-sphere & Merlins
As most Merlin owners know, they have very smooth impedance curves and almost all at 8ohms or higher - they are if nothing else (besides being my favourite speakers)OTL friendly. At the same time, OTLs perform at the best with higher speaker impedance, the higher the better I think. The question is, does adding a Paul Spletz improve things with a speaker like the Merlin, or is it just messsing up a good thing and better left to OTL/speaker matchups that need the help.