Using high powered amp at low volumes power

The signal is likely being attenuated by the pre-amp because
you are listening at low level and not asking for any demand.

I feel that pre-amp will sound best when you can get the
volume level past 1:00 position prefer 2-4:00. That way you
are passing a fuller signal with less attenuation. I would
replace the amp ASAP. (10-25 watt).

Like pacing a jogger in a Ferrari.

You could switch preamps. A passive pre with no gain would help. However, you really only need 10-25 watts as Tom said. My nearfield amp is a whopping 12 watts and I doubt I ever use more than 2-3 watts.

Can be a smearing effect coming from the power distribution. Try swapping power cables if handy.

In my office, I drive my Reference Strada's with a 50W Wadia 151PowerDAC mini. I tried two different Peachtree integrated's including the original Decco which had an amp designed by Scott Nixon. I didn't care for either; not my cup of tea.

BTW: I use a modified Pinnacle SubCompact6 to fill in the bottom end.

If you are running a high power amp at low power levels you will have a problem where the distortion and noise floor of the amplifier is actually higher than you may have expected. Nearly all high power push-pull amps, whether tube or solid state, exhibit this problem.

This can cause the resulting sound to seem somewhat indistinct, unresolved. The solution is to use an amp with less output power or a set of speakers that are less efficient. Since you are so close to the speakers its likely the former rather than the latter.

For low volume levels I would stay away from passive preamplification. Buffered active unity gain as implemented in McCormack preamps is the right choice. I use the lowest gain setting on my preamp which is adjustable.

Quiet volume listening on my setup is little to no compromise:

Mytek digital preamp --> Sunfire 300-II --> Aerial 10T

For some of the recordings I'd benefit from changing the gain settings on my preamp, but would rather not sneak under the chassis everytime I need to do that. User friendly preamp with external gain settings is encouraged after all.

Does anyone know if a (higher end) class D amp such as Audio Research-type would run with less noise than solid state at low volumes if the 'high wattage' was exactly the same? Say 350 watts class D vs. 350 watts class A?

Per design class D amps will have noise in lower volumes.
It dictates that SPEAKERS should be used with low sensitivity.