An Amplifier Change for my Wilson Sophia 2's?

That ARC VT100 would be able to supply to my guesstimate only a third or a quarter of specified power which is only 25...30W realistically at highest volume setting.

I would respectfully but completely disagree with this, Czarivey.

First, most tube amps providing 4 and 8 ohm output taps have the same or similar power ratings when a 4 ohm load is connected to the 4 ohm tap as when an 8 ohm load is connected to the 8 ohm tap. As you realize, a 4 ohm load requires more current but less voltage compared to delivery of the same amount of power into an 8 ohm load. And that difference is accommodated by the different output transformer winding ratios that are used for the two output taps.

In this case the amp is rated at 100 watts, and the measurements provided in Stereophile Volume 20 No. 3 for the original (non-MkII version) of the VT100 confirmed that that rating is essentially accurate for BOTH load impedances, when the corresponding output tap is used. (Aside, that is, for a very slight shortfall of well under 1 db that he measured in one channel, which was suspected to be due to a weak tube).

Furthermore, JA’s measurements of the impedance magnitude and phase angle of an earlier version of the Sophia speaker (linked to below) indicate impedance characteristics that are particularly benign relative to those of many and probably most other speakers that are rated as having nominal impedances of 4 ohms.

www.stereophile.com/content/wilson-audio-specialties-sophia-loudspeaker-measurements

Regards,
-- Al

I've known lots about price categories, but quit worrying about that long time ago.
Sunfire sig 600 was the amp able to make WS speakers literally disappear and bring REAL stage.
If you compare depreciation of 7bst vs. sig 600(both were actually manufactured at nearly same time), 7bst lost near 70% of value getting close to the end of bullet-proof Bryston warranty and sig 600 haven't lost a penny and sold often for higher dollar now than it was new.
That should tell quite something I dare to believe. 
There's no doubt to the quality of that amp despite being one of the first class D amps in high-end audio and if I had $30k+ speakers, I would be more than confident hooking them up to this unit.

Al,

The signal response measurements are done at 1kHz. Therefore for some particular reason called 'X', OP asks the question 'Y' for some same reason everything is perhaps 10...12db hungry of SPL and there's one analogy answer that speaks for itself:

If you have glass of water and you try to fill-up the jar, you will need much more than one glass of water.

The signal response measurements are done at 1kHz.

Most ARC amps have lower effective output impedances than the majority of tube amps, and the VT100 is no exception to that. Specifically, it has a specified damping factor of 11, which for the 4 ohm tap corresponds to an output impedance of approximately 4/11 = 0.36 ohms. Per JA’s measurements the minimum impedance at any frequency of the earlier version of the Sophia is 3.26 ohms, with a near-zero phase angle (i.e., an impedance that is almost purely resistive) at that frequency. And at nearly all other frequencies the impedance is significantly higher.

As you’ll probably realize, the result of the interaction of that kind of amplifier output impedance with those speaker impedance characteristics will be not much different than would occur with a solid-state amplifier, namely very little variation of output voltage as a function of frequency. And yes, in a narrow range of frequencies in the area of about 40 to 50 Hz, where the speaker’s impedance rises to around 14 ohms (assuming the speaker’s impedance characteristics are similar to those of the earlier version of the Sophia), and also in the upper treble region where the impedance also rises significantly, the amplifier’s power capability will therefore probably be significantly less than at 1 kHz. As a result of limitations that presumably would occur in output voltage, however, not as a result of limitations in output current as you had stated.

However in the rest of the deep bass region, as well as in the mid-bass and mid-range regions, which encompasses the regions where most music contains most of its energy, the 1 kHz power capability measurements can be expected to be essentially applicable.

Regards,
-- Al

Wilsons are pretty efficient and you have a fair amount of power. I agree with those who suggest that you may need more gain in your phono or line level preamps. I have heard many Wilsons from Sophia to Alexandria XLF, and they always sounded great with tubes, esp. ARC and VTL. 

I have run Sophia 2's with 30W OTL's (Berning)  60 W OTL's (Atma's)
and class A and AB SS from 40W to 200W and always had plenty of volume. Yes, some differences in sound, but never anything unpleasant.
They are fine floor standing speakers and do well with just about any power.  I guess something may be off in your source or pre amp to amp match.
Or maybe you are chasing high sound volumes that really rock.  In that case my best suggestion is the old original KlipschHorns, and be sure to stick them in the corners of the room.  But do not do that to Sophia's.
Good luck.