Bryston BP20 vs. BP25 questions

My beloved Audire preamp has bit the dust. I have been contemplating a move to Bryston for a while now, anyway. This just makes it necessary. Before pulling the trigger on a good used BP20 or BP25, I have two sets of questions and I can’t seem to find any answer for them.
The first set involves the volume control on the BP25. A little background,,,, I have a quadraphonic set-up and due to a large amount of downstream components, the volume settings on my primary preamp (the Audire or the Bryston) are rather delicate. The Audire preamp features 10 very helpful graduation marking lines around the volume control, (sure wish Bryston did the same). Currently, the difference on the Audire volume setting between 3.0, 3.1, and 3.25 (out of 10) can run the gamut from too soft at 3.0, to too loud at 3.25. And every album or CD likes to have its own volume setting.

So, my first questions involve the BP25 volume control:
1a) I understand that it can be controlled by the remote. Can it also be controlled by turning the knob?
1b) Does the knob turn when you use the remote? No matter how you might change the volume setting, does the line on the knob always go back to the same setting when you zero out the volume? (like about the 7 o’clock position?) So, will I be able to count of the fact that the 9 o’clock position by the volume pointer line will always be the same volume? Likewise the 12 o’clock position will always produce the same amount of volume – or do these settings slide around?
1c) Also with the volume control – is the attenuator stepped or smooth? If it is stepped but has 40+ steps it would work for me, but if it has less than 35 steps that would probably be a deal breaker.
1d) Lastly on the volume, can you move it ever-so-slightly using the remote; or is it hard to move a really small amount?

These questions would not be necessary if I was more familiar with the BP 20 line, namely, the power supply. Ultimately, if I go the BP20 route I would want to obtain a BP20 with a MPS-1. I could add a MPS-1 later if the BP20 would accept the change.
Now my BP20 question:
2) Somehow I get the idea that, not all BP20s are capable of accepting the MSP-1 upgrade if the BP20 originally came with a BP-PSR. Is that correct, or will a MPS-1 work with all BP20s?

Thanks in advance.