Agreed, this warning will be included in all of my/our future product manuals that use BTL class D technology... thanks to the reminder by the TB community.
Why support anything that's not a passive speaker being hooked up to the output of the amp? Especially since new class-d power output can be very high voltage and current - it's not safe hooking up anything else.
When you think about it, there's no advantage, DI from the pre-amp is in the feedback path from the output of the amp to the input (properly isolated) and thus any speaker interaction is part of the pre-amp DI output.
The DI itself should be properly isolated and not subject to any normal voltages that could be on the line like phantom power.
Anybody can add a transformer to the ID circuit. Or gee, add some extra EQ to the DI only out.
I'm sticking with the Milbert assertion that if transformers are so good for sound why not do these things have 3 or 5 transformers in them?
Yeah, sure, only 1 is needed to add all the magic, but me I prefer that pre-amp add the magic, and I'll black-box it and don't care what's inside if it's the sound I want.