Bi-amping vs. bridging

Using an amplifier in bridged mode causes it to "see" a load impedance equal to half of the speaker’s actual impedance. The Motion 20’s nominal impedance of 4 ohms would be seen by a bridged amp as 2 ohms. I doubt that your amp could handle a 2 ohm load with good sonic results. And I wouldn’t be surprised if the amp’s self-protection mechanisms were triggered if it was operated in that condition, causing the amp to shut down.

It might be a different story with the IQ5, which has an 8 ohm nominal impedance. But I suspect that even in that case you would get better sonic results, albeit probably a bit less power, via biamping.

Regards,
-- Al

P.S: Although it probably won’t be an issue, especially if your preamp (or whatever component is driving the amp) is solid state rather than tube-based, a point to be aware of regarding biamping is that since the preamp will be driving two amp channels for each speaker it will see the amp’s input impedance divided by two. Unless, that is, it provides four or more channels, or it is one of the rare two-channel preamp designs which provide two pairs of output jacks for each channel ***and drives each of them with a separate output circuit,*** rather than the much more common approach of simply connecting them together and driving them with the same output circuit. (Asterisks added for emphasis).

Regards,
-- Al

Good stuff for sure Al.  Thanks for the insight.  My pre/pro is the Marantz AV-7005.  It's handling the bi-amping of the Kef's at the moment, without any issues I'm aware of.  I have yet to place the ML's into the mix.  So, should I be using the Front High or Front Wide for the second channel for the tweets?