My friend recently got a pair of Focal Maestro Utopia. Magnificent speakers, a bit pricey and also a bit heavy. In the shop we tried them with an AVM power amp, which shut down unexpectedly. The Maestro's impedance minimum is 1.7 Ohms around 100 Hz. My M-4 did quite well. It did not show problems driving such a difficult load. Of course, it lacked power. I did not try the M-2 and B-6 as they are stated "8-16 Ohms" only. My friend then got an almost NOS CX-1/MX-1 combo. I tell you, the MX-1 is really a beast. IMHO totally underestimated. After one hour of listening to Rammstein at *authentic levels* it was only handwarm. So, if you own speakers which are a difficult load, get an MX-1.