My **guess** is that you’ll be ok pairing the XA25 with the ML 11A if your room is of average size or less, and if (as appears to be the case) your listening does not include recordings having extremely wide dynamic range (such as some classical symphonic recordings that have been engineered with minimal or no dynamic compression). Especially given that the speakers incorporate powered woofers which are crossed over at 300 Hz.
I do have some uncertainty, though, stemming from three things:
1) Stereophile measured the sensitivity of the somewhat larger ML 15A speaker (which also incorporates a powered woofer crossed over at 300 Hz) as being 87 db/2.83 volts/1 meter, which is 5 db less than the 92 db/2.83 volts/1 meter spec of that speaker.
2) The 4 ohm nominal impedance of both the 15A and the 11A means that on a per watt basis their efficiencies are 3 db less than their 2.83 volt sensitivities (since 2.83 volts into 4 ohms corresponds to 2 watts).
So it appears quite possible that the efficiency of your speakers may be as low as 91 - 5 -3 = 83 db/1 watt/1 meter.
On the other hand, though, per John Atkinson’s measurements the XA25 is capable of delivering 130 watts into 4 ohms, with the 80 watt delta relative to the amp’s official rating of 50 watts for a 4 ohm load being due in part to Pass basing their power rating on much lower distortion percentages than JA bases his measurements on, and in part to the amp transitioning from class A to class AB at some power level (that I presume is not a lot higher than 50 watts).
3) JA found that the amp’s distortion performance degrades somewhat in the treble region when the load impedance drops to low values at high frequencies. And the 11A’s impedance descends to 0.6 ohms at 20 kHz.
So, again, my guess is that you would be ok pairing an XA25 with your speakers, given your listening habits and assuming your room is not particularly large. But there are reasons to be uncertain about that.
Good luck, however you decide to proceed. Regards,
-- Al
