Configuration Questions

I do not understand your post. If it is an integrated amp then it has a volume control; what is it you are setting at 1.5 if not a volume control? Why do you need to use 2 preamps; that is what you are doing? Do you mean it does not have a REMOTE volume control? In theory you should open one volume control all the way as that takes it out of the circuit to a great degree. In practice results will vary with the gear involved. If the pre has a remote I would try the int. vol. control wide open and start the Creek at the bottom and see how this works but as I say do it the way YOU think sounds best. All line level inputs on the MF SHOULD be the same so you could use any but the phono input if it has one. I use to sell A-1s but it was long ago and far away.

Please check you MF piece again, sounds like you have a MF power amp and not an integrated amp, unless your B1 is missing the volume control...I had a MF B1 for a very short time

I'm sorry--I'm adding the Creek preamp solely for the remote control. The B1 is indeed an integrated amp.

So the question, then, what is the best volume configuration. If the B1 is cranked full open, that would result in background noise to some degree.

I'm not sure about behavior of the so-called passive preamps; do they like operating at the higher volume level or no? Also, what does that mean for the signal that sends to the B1 amp?

Integrated amps having no pre out/amp in jacks leaves your method as the only way to use your components as you wish. You will however have to play with the volume control on both the amp and the preamp levels to find the best medium of signal to noise.
How do you like your Dac Magic? I am considering it.