I totally agree with Atmasphere's balanced/differential observations. That's how the Ref 3 shows its full potential.
However I am not so sure on the impedance-match limitation.
The Aleph 5 input is only 25Kohm balanced differential, quite bellow the 100Kohm suggested mark. It's a great match with my easy speakers. Magic midrange and great dynamics.
Additionaly, if you check Stereopile's measurements of the Ref 3, it is inferred the distortion is very low on loads above 10Kohm.
As stated before, the most common mismatch is power-amp/speakers.
A dealer is announcing a new Ref 75 power amp (only balanced inputs as usual in the Ref series). Although quite expensive, this may also be a great match.