I've sent an email to miniDSP to see if they can clarify their manual instructions in terms of output levels and Dirac. I'll be the first to admit I'm wrong if so, and that would be great news for folks like me and
@Kachda who understood it the same way. The miniDSP forums also talk about this -10db volume setting as well, fwiw, so it's not just us.
If you use a target response that is at or lower than your initial measured response Dirac will cut, not boost. In any case it is very easy to measure the amount of boost that Dirac is applying by doing a loopback with REW using the SHD as the USB input/output on your computer. This will also give some interesting insight in to what Dirac is actually doing. It is likely that the applied boost is much less than 10 dB.
Assuming you are using the SHD as volume control Dirac boost is also much less of an issue. If you do not have enough output at -10 dB that means your input is much less than 0 dB and it is perfectly safe turning the volume up. To me Dirac boost is really only an issue where you are running the SHD at 0 dB and using downstream volume control.
To your specific case you mention an amplifier input sensitivity of 1.43V. Applying -10 dB to the 4V SHD output gives 1.26V, so although you will not be able to clip your amplifier at these levels you are really close (~1 dB).
EDIT: Should have stated the obvious but the example above regarding the amplifier with 1.43V input sensitivity assumes that NO boost is applied. If you apply even 2 dB of boost it is
possible to clip your amplifier even at a volume setting of -10 dB. Short story is 4V output voltage is more than enough to drive most amplifiers in to clipping even with some attenuation.
Michael