How do you categorize amplifier with an output transformer?OTL?Are we going in circle?or we might just go back to SE or PP.The mean reason why these amp were design is that they will work without OPT.Again, what we found after getting into the business is that some people wanted to use our amps with really low impedance speakers. The combination was non-functional. Like many tube amps, OTLs don't like low impedance loads. So what to do? If the customer really wants to use the OTL with that kind of speaker then you make it possible by using a set of ZEROs.
In some cases its just the woofer section that might have the low impedance. In such cases you can install the ZEROs so the amp is driving the mids and highs directly while using the ZEROs to deal with the lower impedance of the woofer array.
The ZERO is intended as a problem solver plain and simple.