My suspicion is that the REF 3 design includes active circuitry that is "ahead" of the volume control in its internal signal path. If so, the fact that the volume can be cranked up to high levels without clipping when a SUT is not being used would still be consistent with the clipping occurring in the REF 3 rather than in the phono stage.
IMO there is no reason to be concerned about using the volume control at 2/3 max or other relatively high settings within its range. In fact that is considered by some to be generally preferable, as in some designs it might minimize whatever sonic side-effects may be introduced by the volume control mechanism itself.
So I would simply go without the SUTs. Keep in mind, of course, that without the SUTs the resistive load setting in the phono stage that is sonically optimal stands a good chance of being lower than the setting(s) you use with them.
Regards,
-- Al
IMO there is no reason to be concerned about using the volume control at 2/3 max or other relatively high settings within its range. In fact that is considered by some to be generally preferable, as in some designs it might minimize whatever sonic side-effects may be introduced by the volume control mechanism itself.
So I would simply go without the SUTs. Keep in mind, of course, that without the SUTs the resistive load setting in the phono stage that is sonically optimal stands a good chance of being lower than the setting(s) you use with them.
Regards,
-- Al