In message , "Dave Plowman (News)"
writes
Wanting to experiment further, got a Behringer DCX2496 which is a
direct substitute, but digital, so allows a choice of crossover curves,
delays to each unit, and EQ too.

First impression, setting it to the same as the analogue one, was no
audible difference, which is good.

But slowly, when left on, it developed a buzz from the speaker(s) Loud
enough to be annoying.

Approach the speaker and the buzz drops in level and get close enough
and it goes. So you can play it with a hand rather like a Theramin. ;-)

I'm way out of date, so unlikely to offer anything worthwhile, but

1. are you feeding this speaker from a balanced or unbalanced source?
2. Does the hum stop if you disconnect the source?
3. Where, if anywhere are mains and xLR grounds connected together?

I'm a transformer man, so servo balancing sounds like a black art or
hole to me.
--
Bill