Since the miniDSP and FIR filter is messing with my signal, let's look at the output of the preamp.
(This measurement includes a 25 foot RCA to 1/8" miniplug from preamp to PC onboard sound device, and any defects caused by them.)
Blue is without the filter, and green is with. Basically no difference in frequency response is seen, results within .1dB or so. (Flat dark blue line is just the measurement cursor)
The FIR filter is changing phase, so here is that measurement at the preamp:
Blue is the preamp output without the filter, green is preamp output with the phase correction filter applied.
And finally, for right now...
Top green is the in-room measurement of phase with the FIR filter, red is the unfiltered room measurement of phase, and the lower green is the phase correction applied at the preamp by the filter (as measured at the preamp out).
This shows how the FIR filter creates* a reasonable inverse to the phase error detected in the room, and applied that to the signal, and corrected the sound in the room.
*rePhase is a manual tool, so the inverse isn't perfect, I have to move a lot of sliders and mess with things a while to have gotten it that close