As I am one of those who have commented on the LS 16 MK II in Audioreview.com concerning power supply limitations and the effect in terms of dynamic bass swings, I thought I should add a few comments here. The transformer is not attached to the circuit-board; it is bolted on to the side of the unit, but there is a captive circuit board that takes the outputs from the transformer. I believe that it is a 35 VA transformer, compared with a 45 VA unit in the LS 25, and a 50 watt toroidal in the SP9 (any version).
The size of the transformer reflects cost compromises, but also the priority that Audio Research puts on transformer size. The capacitors in the unit are described by Audio Research as "expensive" or "costly" or words to that effect, and cost savings at that end could have purchased a larger transformer.
In order to get the best sound out of the unit, there should be a good sound conditioner used. This improves bass impact; eliminates an infrequent stressed quality to the midrange; and results in a blacker background. The unit is VERY sensitive in this regard, but so too is my SP 9 MK III, which has a large toroidal transformer (and which I still use as a phono premap). I use the unit with the Monster 5000 sound conditioner, classe cable, and at its IEC input, the last version of the VESA block sound filter. Removing any of these from the chain reduces bass impact, dynamics in the context of heavy bass recordings (CD not LP, and not very many CDs), and results in a less black background, or one might say, a lesser sense of ease. The sensitivity to line conditions is, I suspect, in part a function of the limitations on its power supply regulation: a smaller transformer results in higher power supply impedance, whatever one might say about the quality of the regulation circuitry that follows it. Having said that, I suspect that most preamps would benefit from a cleaned up power line, although probably not to the same extent.
I use the unit with the Audio Research VT 100 MK II, and as a line section is sounds MUCH better than the line section in the SP9 MK III (as it should, for the cost). Also, it sounds substantially better using its balanced outputs when driving the Audio Research VT 100 MK II (with the MK III there is said to be virtually no difference between the sound from the balanced and the SE inputs).
I hope this helps.