I understand your point and the significant importance of the output transformer. In threads discussing tube amplifiers I consistently advocate the undeniable need for high quality transformers if one is seeking excellent sound quality from tube powered amplifiers.
My point is if you look at the Sony SS AR1 speaker measurements they are as George and others have rightly noted, a ’challenging ’ speaker load given its impedance curve and phase angle characteristics. Armed with this knowledge the last thing you’d recommend is a 14 watt tube amplifier.
The low watt tube Luxman is doing something obviously good that can’t be surmised from assessing its measurements or those of the Sony. So again, how is this gross mismatch (Via documented measurements for both products) able to produce such high quality sound? Something is occurring that isn’t accounted for with supporting test bench numbers.