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@mesch Speaker sensitivity AND impedance/phase angle are to be considered jointly as to the ability of an amplifier to power the speakers unlike the @millercarbon statement. I own speakers with a 98db sensitivity that have a low impedance of 3.2 ohms and sharp phase angles there which allow 30 watt tube amps to play it beautifully and 200 watt solid state amps which cannot. Apparently, the impedance/phase angle has more impact on amps and my speakers than sensitivity.

Also, I personally know of reviewers who publish high end equipment reviews so that they can have equipment to resell.

As to the VAC 170IQ review, I was also shocked at how poorly it measured which reminded me of the recent Cary amp review of similar disrepute. In the Cary amp instance, the reviewer found that it sounded very good. There is a dictum which states that if something sounds good but measures poorly, someone is measuring the wrong thing. However, there could be a defective product (EAR Classic had such a review, later corrected-it is a very good sounding CD player) which caused the poor measurements. I want to hear from users and the manufacturer as to why the VAC 170IQ measurements stunk.

I have no opinion as I have not read the review, however it may be sample variation, as you have surmised, because Stereo Magazine found that it measured well

https://stereo-magazine.com/archive/articles?tx_archive_pi1%5Baction%5D=download&tx_archive_pi1%5Barticle%5D=69341&tx_archive_pi1%5Bcontroller%5D=Archive&cHash=b63605b6cab9c40ddc6dbc5e2d1dd3ed

‘Low distortion, low noise, high bandwidth and
an enormous attenuation factor for a tube amplifier.’

Hope this helps.

Did they measure-the same one they reviewed?

It is interesting that the stereo-magazine.com article does not indicate the distortion level at 64/65 watt continuous output as well as other problems Atkinson found.   https://www.stereophile.com/content/vac-sigma-170i-iq-integrated-amplifier-measurements  However, on-line I just read multiple explanations that point to a need to carefully select a partnering speaker, preferably above 90db efficiency and easier impedance phase angles.  This is rated as an 85 watt amp but reaches 3% THD on a slow rise at 51 watts, 2nd harmonic distortion type which may not be hearable versus a similar solid state amplifier with the same distortion but with a quick rise.  Herb Reichert, Jim Austin and John Atkinson further explain the measurements.   They were answering @George who stated from the review  "Using our definition of clipping, which is when the output's THD+noise percentage reaches 1%, the amplifier with both channels driven with a 1kHz signal clipped at 11.8Wpc into 8 ohms."   I can't say George doesn't have a good argument that the amp section is very particular of it's speaker mate with a low damping factor and high impedance resulting is potentially great frequency response variations.

I think Jim Austin gave a pretty good account of the design intent: ie deliberately eschewing feedback in the interests of improved SQ into tube friendly speakers - rather than designing a panacea for all speakers. It‘s also interesting to note that Jim confirms that an amp that measures worse (ie without feedback) can actually sound better.

He also made the interesting point that some speakers like to see high output impedances. From memory, I think these these mainly fall into the single driver category. Speaker matching is always important to a certain degree.

@fleschler  I agree entirely regarding sensitivity and impedance/phase angle effects on the in room efficiency of a speaker. I have read many speaker reviews that don't adequately address this.