Quad Owner posting. (21Ls) 1 I have not heard the Monitor Audio but I want to echo what the firstname.lastname@example.org has written. I have heard the 12Ls and the 11Ls as well.
The Quad's are very very sensitive to upstream equipment. If there is a bright component or an 'etched' sounding cable in your signal path the Quad's will be very fatiguing - I suspect the exact same of the Monitor Audios as they are also very good quality speakers.
My Quads were very fatiguing until I fixed my system.
NAD C350 - Black Rhodium AST 200 Bi-Wire - Pioneer DV353 - Monster Interlink MkII Interconnect.
I now HAVE:
NAD C350 - FT Audio LW1S2 Passive Pre-Amp - Kimber 4strand Copper OEM Interconnect with WBT clone ends between source and pre-amp and another run between pre-amp and amplifier - NearSota Speaker Wire in bi-wire configuration - Toshiba SD-430V [Both Source and Amplifier are to be replaced as soon as funds allow]
I have tried a large number of sources and a few amplifiers with my speakers. (See my post history for in home CD player Comparison Roksan/Rega/Cary/Creek/Cambridge/Arcam)
I am not the only Quad owner I know to have serious issues with Black Rhodium and the Quads and cannot in good concious recommend them to any Quad owner. Only now having transformed my system, with more improvements on the way - is the system musical, involving, detailed with a decent soundstage (although my poorly designed room is playing havoc with that).
Again, and something most people forget, The Speaker is NOT the most important component in the signal chain. Your speaker is ONLY as good as what it is fed. You spend 80% of your budget on speakers, great fantastic, but if your feeding it from poor quality components through poor quality interconnects that expensive speaker will sound horrible. Garbage in Garbage out. Speakers are not capable of correcting poor quality amplification or data being sent to them. Some speakers are more sensitive to poor quality equipment than others. Quad's are sensitive to this, and again probably so are the Monitor Audio's.
I'm sure the Quad's will sound very nice, and so will the Monitor Audio Gold 10s try to audition them in your home if possible and also be cognizant of the impact that other components can have upon your listening experience.
Anyone can e-mail me to talk about this or the Quad's if they'd like.