I have my eye on a pair of Rotel RB06 power amps. They are stereo, but
by oving a few jumpers can be used in bridged mono configuration.

However, although in stereo mode they can drive 4 and 8 ohm speakers,
apparently in bridged mode they cannot be used on anything below 8
ohms, ruling out their use on my Dynaudios.

Can anyone briefly explain why this is the case? I have no reason to
disbelieve the Rotel manual and the nice bloke I spoke to on the phone
at Rotel, but would like someone to put into plain English the
technology behind it. Thanks.